Necessity is the mother of invention.
—Plato, The Republic
WHILE THE TRENDS TO WARD MORE energy-intensive water and more water-intensive energy carry a sense of foreboding, thankfully there are several different technical solutions that exist. These options include source switching, advanced technologies that reduce resource intensity, smart technologies that increase information intensity, distributed technologies, and integration of our water and energy systems so that one benefits the other. In some cases these solutions are already being implemented somewhere worldwide, and just need broader adoption. In other cases, much innovation remains to be done. However, all of these are plausible and technically feasible.
Some of the solutions have catchy slogans. “More crop per drop” for efficient water use in agriculture, “showers to flowers” for using graywater in our homes to irrigate our lawns and gardens, and “toilet to tap” for turning reclaimed wastewater effluent into drinking water. For whatever reason, similar slogans for the energy world have not been developed. Regardless, these and other approaches are worth pursuing.
Source switching means choosing energy sources with reduced water intensity or water sources with reduced energy intensity. Fuel switching can be accomplished in a variety of ways and has been done with a variety of motivations. In the 1970s, in response to the oil shocks, rampant fuel switching took place nationwide, to get away from the volatility and supply risks of petroleum and move toward other options. In the power sector, utilities switched from oil, which at its peak was responsible for 17 percent of our electricity generation, to natural gas, coal, and nuclear. By 2015, petroleum was below 1 percent of the fuel mix for the power sector. The industrial sector switched from petroleum to natural gas for process heat. And the residential sector, which had switched from coal to heating oil only a few decades before, started switching from heating oil to natural gas and electric heat. Many homes in the northeastern United States still use heating oil today, but the transition continues.
These shifts in the energy mix occurred for national security or economic reasons, but they also have environmental implications as we switch from dirtier to cleaner fuels or the other way around. Shifts also have water impacts. Consequently, we could intentionally shift our fuel mix to one that has lower water requirements.
In the power sector, many power plants built in the 1970s and 1980s are due for retirement or retrofit. These power plants are overwhelmingly coal and nuclear, built at a time when concerns about water scarcity were muted. In 1970, there were only 200 million people in the United States, compared with well over 300 million today. At the same time, that was a relatively wet decade. Because there was more water being used by fewer people, the power sector was not designed with water efficiency in mind. Planners at the time did not properly forecast the water strains that would occur from population growth, economic growth, and climate change.
Many of those power plants are very water intensive, with thirsty open-loop cooling systems designed around the steam cycle that was developed in the late 1800s. Since most power plants are designed and built for a nominal forty-year lifespan, many of those are coming to the end of their useful operation. To keep them going, substantial investment will be required, so most power plant operators are at a point where they must decide whether to retire or retrofit their power plants.
Nuclear power is very water intensive, so switching away from it would be a benefit from a water perspective. However, nuclear power plants are likely to have their operational lifetimes extended by at least twenty years for a variety of reasons. First, it is difficult to build new nuclear plants, and so extending the licenses of existing plants is usually a more straightforward path. Furthermore, already-built nuclear power systems are usually cost competitive, whereas new ones might not be because of their high capital cost for construction. Last, nuclear power plants, which do not have smokestacks, are well positioned to remain competitive as environmental standards tighten for emissions.
The story is different for coal. In addition to being very thirsty, many older coal plants are also very dirty: they emit high volumes of carbon dioxide, particulate matter, and mercury, which makes them vulnerable to more stringent emissions rules. Thus, the older coal plants are ripe for retirement. Phasing out those old coal plants and switching to natural gas combined cycle, solar panel systems, and wind farms all would spare significant volumes of water. Even when considering that natural gas produced by hydraulic fracturing from shale formations needs more water than coal mining, the reduced water use at the power plant because of the increased efficiency, avoided emissions controls, and partial air cooling for the combined cycle make the switch from old coal to new natural gas combined cycle plants a significant water saver overall.1 The same approach is also relevant for the transportation sector: switching from petroleum to natural gas can save water, as could switching first-generation biofuels made from corn back either to petroleum or to biofuels that do not require irrigation such as sugar cane or cellulosic sources such as switchgrass.
Just as switching the energy source can save water, changing the water source can save energy or freshwater or potentially both. In particular, reusing water can be an appealing option. There is an Arabian proverb: “In the desert, any water will do.” That includes degraded water: brackish water, saline water, graywater, and treated effluent.
If homes are built with distinct plumbing systems that separate the water streams, then the domestic graywater from showers, sinks, and clothes washers can be used within the home. Graywater can flush toilets inside the home or water our flowerbeds outside. Since it is not necessary to use the most energy-intensive form of treated drinking water for these applications, graywater usually represents an energy savings for nonpotable applications. In many ways it is ridiculous that we use the world’s cleanest water for toilet flushing in the first place, so this approach seems sensible by comparison. With minimal treatment to remove the organic components, it can also be used again for washing. While graywater reuse can help avoid using the most energy-intensive water, if everyone does it at a large scale, then the sewers might not have enough water to operate effectively. These kinds of unintended consequences should be planned for. In addition, rainwater can be collected from storm runoff through roof systems of gutters into rain barrels. That water can then be used for irrigation. Notably, while rainwater might be very clean when it lands on the roof, it subsequently might pick up chemicals that make it unsafe to drink.
It is also important to note that if you have a graywater system at your home, then it would be good to use biodegradable soaps and avoid putting toxics down your drains, lest they end up on your plants a few hours later. The International Plumbing Code, which is only used in certain jurisdictions in the United States, allows for graywater from showers and bathtubs to be used for flushing toilets. However, the Uniform Plumbing Code, which is used more widely in the United States, prohibits graywater use indoors.
Harvesting graywater is not only a way to supply more water, it is also an option for harvesting heat. While the graywater from toilets generally is not heated—though some fancy Japanese toilets have heated water for user comfort—the water from sinks, showers, and laundry machines is often still hot when it goes down the drain. That heat is typically lost through the pipes to the ground as the wastewater moves along. However, with a heat recovery device, it can be used to preheat incoming freshwater to the water heater tank, saving energy.
Overall, graywater use can spare some freshwater withdrawals and might save energy for heating, pumping, and treatment. For some rural settings where water is really scarce, graywater might also be contemplated as a source of potable water. In these cases, graywater reuse for potable needs might actually be more energy intensive than getting freshwater straight from a well.2 Many rural areas get water from wells, especially for remote domestic purposes or many small farms or ranches. For these applications, the groundwater is often very clean, and so the energy requirements are simply for pumping. By contrast, graywater reuse for potable purposes would require additional treatment to remove the organic components and pathogens, driving its energy intensity higher than simple pumping. In those cases it makes more sense to use the graywater only for irrigation. However, in municipal areas that already have advanced water treatment systems in place, graywater reuse could make a lot of sense.
One of the approaches to solve this crisis is to put the waste streams from the energy and water systems to useful purpose. There are a variety of ways to accomplish this goal. In particular, there are 30–40 billion gallons of treated effluent generated each day in the United States.3 Because the wastewater is generated in cities, the wastewater plants are nearby. That means the effluent is an abundant source of water that is generally colocated with population centers. And, it is typically overlooked as a source. If that treated effluent is “reclaimed”—or used again—it can be a reliable supply of water. Reclaimed water is distributed in purple piping systems so that it can be distinguished from the treated drinking water and sewage.
Effluent is usually returned to lakes or rivers, or ejected into aquifers or oceans. While our ecosystems depend on many of those returns, it is also possible to use the effluent again before returning it to the watershed—for example, running the effluent through a power plant as a source of coolant. If the water does not need to be returned to a nearby river then it could be used for consumptive purposes as an alternative to freshwater—for example, for irrigating crops, hydraulic fracturing, or industrial purposes. The “toilet to tap” idea introduced earlier is a robust one. That approach saves energy compared with desalination to make brackish water or seawater potable. As it is already in place around the world in places like Singapore, Israel, and Southern California, and out of this world aboard the International Space Station, it is a proven technology.
For many municipalities, closing the loop with their waste streams to turn the wastewater into drinking water or for other water purposes might make a lot more sense from an economic or energetic perspective. Austin, Texas, has set up an extensive purple-piping network that brings the treated effluent from the wastewater treatment plant to downtown Austin, some high-density neighborhoods near the urban core, and the University of Texas, where it is available for irrigation and cooling. This approach is sensible since drinking water is not needed for these applications and because treated effluent in Austin is much cheaper to buy than drinking water. The original customers for the effluent were local golf courses that used the water for their extensive irrigation requirements. Since then, more customers have emerged for the water. The effluent can be used within buildings for nonpotable purposes such as toilet flushing. In this case rather than “toilet-to-tap” it would be “toilet-to-toilet.” For organizations that have the up-front capital to invest in the purple-piping infrastructure such as the city of Austin or the University of Texas, reusing effluent is a cost-effective option.4 Generally speaking, reuse projects are more expensive than water conservation programs, yet more affordable than seawater desalination.5 It is also a resilient, drought-resistant source of water supply. However, despite those benefits, it does pose some financial, health, and performance risks. Just one risk is the possibility that the purple-piping system will accidentally get cross-connected with the drinking water system, meaning treated effluent that isn’t intended for drinking will be used for potable applications. And the billing rates for reclaimed water are typically set at a level below what is needed to recover the full costs of building the system, which means the customers are subsidized. While those customers surely benefit from the lower costs, the discounted rates put the long-term financial health of the reclaimed water system at risk.6
Treating wastewater effluent to a standard such that it is suitable for drinking is sometimes called “toilet to tap,” which should not be confused with actually drinking water out of the toilet. It is not clear why a warning sign is necessary: who would drink toilet water? [Photo by Ashlynn S. Stillwell]
One place where effluent can displace the use of freshwater is energy production. In particular, hydraulic fracturing is a rapidly growing technique that uses water to improve productivity from wells in many more locations than before. In some areas, those water needs are competing with other users. At the same time, hydraulic fracturing does not require drinking water or even freshwater, for that matter. Effluent might be a useful alternative, and its use has already been demonstrated by some shale producers in Texas, where water scarcity encourages experimentation with water alternatives.
Effluent can also be used for power plant cooling.7 In 2010, there were already forty-six power plants out of more than a thousand power plants in the United States that used reclaimed water for cooling tower makeup. Another handful of facilities use reclaimed water for cooling ponds, air scrubbers, as injected pressure at geothermal fields, and as boiler feedwater. Those include the very large nuclear power plants at Palo Verde in Arizona, which use the municipal wastewater from Phoenix and other cities nearby. While reclaimed water was first used for power plant cooling in 1967 in Burbank, California, in total only about a dozen of these cooling systems were built before 1990. After that, the pace of using effluent for cooling water accelerated, reflecting the increasing pressures on water resources in general.
Generally, effluent is safe to use for power plant cooling, although some minimum secondary treatments are recommended for disinfection and to prevent problems with equipment. For example, additional treatment can be useful as a way to prevent scaling, corrosion, fouling, foaming, or biological growth, all of which can degrade performance. In addition, there are concerns that windblown spray from the use of reclaimed water for cooling might reach workers or the general public, a risk which can be mitigated by setting the cooling tower at least ninety meters from the public or using higher levels of disinfection.
A general rule of thumb is that it makes sense to ship reclaimed water up to twenty-five miles for power plant cooling, beyond which the pumping requirements outweigh the benefits. In places where water is scarcer, then the twenty-five-mile rule is not as relevant. For example, the Palo Verde plants, located in a desert, must pipe the reclaimed water dozens of miles from the treatment facility to the power plant. The cities of Phoenix, Glendale, Scottsdale, Tempe, Mesa, and Tolleson all provide the wastewater for the power plant.8 The wastewater from Phoenix moves nearly thirty miles downhill using the force of gravity, then is pumped uphill for eight miles to the nuclear facility. The other wastewater streams move even farther, up to sixty miles in some cases. Although that seems like a long distance, it is much shorter than the hundreds of miles that freshwater is piped from the Colorado River. Palo Verde is the only nuclear facility that uses 100 percent reclaimed water for its cooling. It is also the only nuclear facility whose cooling systems do not return water to the environment. The water reclamation facility can handle a total flow of 90 million gallons per day, and uses 25 billion gallons annually. And, while the power plant operators are willing to pay a high price and would like more wastewater, they now face competition from cities and other industrial users, who also want that water.
Scaling up the idea at other plants, the tens of billions of gallons of wastewater generated each day across the United States are more than enough to satisfy the billions of gallons of water consumed each day at power plants. The question of practicality becomes one of distance, cost, and other tradeoffs. While the total flow of treated wastewater is sufficient to meet the total consumption needs of power plants, there could be a spatial or temporal mismatch that prevents its convenient use. For example, large wastewater treatment plants and large power plants might not be close to each other. Or, the times of day or year when wastewater flows are highest may not correspond with the times of day or year when water is needed the most by power plants. And, many regions rely on wastewater discharges to streams, lakes, or aquifers. Diverting those discharges for power plant use instead might deprive those ecosystems of badly needed water. Despite these obstacles, it is clear that using reclaimed water for power plant cooling remains mostly an untapped opportunity. While only a few dozen plants use effluent today, there are hundreds that could.
Effluent can also be used for nonpotable industrial processes, such as firefighting, or as a heat transfer fluid in the form of steam for distributing heat or chilled water for cooling. And water is a necessary ingredient for snowmaking for ski resorts. Larger ski resorts often use snowmaking to increase the skiable terrain or to extend their operable season. A posh ski resort in Killington, Vermont, that caters to Bostonians and New Yorkers looking for a large ski hill within a half-day’s drive of their city, uses its snowmaking as a key selling point. The snowmaking system uses more than 720,000 gallons of water per hour at full force, operates 1,500 snow guns with eighty-eight miles of pipe, and can add one foot of snow to eighty acres over the course of an hour. Killington uses effluent as its water source for snowmaking, noting in its promotional materials that it has “a virtually endless supply of water.”9 As wastewater is continuously generated, this claim is true.
And while effluent has its advantages in supply and cost, its use can generate criticism. When Killington first announced this plan in 1987, detractors poking fun at Killington created a fake organization named “Vermont Association for Sanitary Skiing” to generate opposition; they also created the bumper sticker “Killington: where the affluent meet the effluent.”10 This clever slogan is reminiscent of the “toilet to tap” phrasing in terms of its intent to generate a negative impression. And it worked: several Vermonters whom I befriended while writing this book over the river at Dartmouth College said they would never ski at Killington for precisely this reason. However, it turns out that Killington was simply decades ahead of its time in recognizing that properly managing a scarce resource is a sensible thing to do. Using effluent also offered cost savings compared with building reservoirs or using municipal drinking water. The snowmaking was good for business because it helped improve skiing conditions and allowed the resort to extend its ski season, both of which increased revenues. This case is yet another example of how thoughtful management of resources can carry economic and environmental benefits simultaneously.
Interestingly enough, one of the initial critics—Bill Mares, who was one half of a duo of legislators who were poking fun with their bogus organization and clever slogan—issued a public apology in 2012 for the gimmick. In an interview, he noted that he and his legislator compatriot found the whole episode amusing, but twenty-five years later in the context of heightened awareness of water scarcity, he admitted, “Now the joke is on me. Killington was way ahead of its time.”11
Demonstrating the point, the idea found traction elsewhere. Arizona Snowbowl, a ski resort in the desert Southwest, announced its plans in early 2012 to “become the first ski resort in the world to use 100 percent sewage effluent to make artificial snow.”12 This situation raised protests because of health concerns. For example, what happens when skiers fall and accidentally ingest the snow? And, compounding difficulties, the mountain is sacred to the local Navajo tribe; spreading sewage on the mountain is equivalent to desecration.
Just as effluent or reclaimed water can be used to save energy and spare freshwater resources, the same can be done by using brackish or saline water as alternatives. Brackish or saline water can be used as droughtresistant sources of drinking water. Some of these sources are not obvious. For example, mine pool water from underground coal mines could be used—and in some cases is already used—by some power plants near coal mines in Pennsylvania and West Virginia.13
There are more than thirteen hundred power plants in the United States, about a thousand of which report their water use data to the U.S. government.14 Of those, about 10 percent use either brackish or saline water. In total, forty-nine use brackish water (six from aquifers, forty-three from surface sources), and forty-seven use saline (two from groundwater, forty-three from surface water, and the remainder from “other” or plant discharge). Most of these power plants that use brackish or saline surface sources are coastal power plants that can use seawater. Seawater has the advantage of generally being cooler and abundant. Groundwater sources means the water is being pulled from brackish or saline aquifers, though it is unclear whether any water is being returned to the aquifers by the power plants.
As with effluent, there are some challenges with brackish and saline water for its users. For example, they are more corrosive than freshwater, which means better design and more expensive materials might be required. Sometimes demineralization helps, after which salt disposal is a burden. Also, coastal saline water is part of an ecosystem, so biofouling is important to monitor. Overall, the use of brackish or saline water for power plant cooling spares a lot of freshwater. The same could be said for hydraulic fracturing. While producers prefer to use freshwater to which an assortment of chemicals are added, there are some reports that brackish and saline water can also be used effectively.
For drinking water, desalination remains an option but is still limited. Solving its problems will help make it a robust option for societies. It is still expensive and energy intensive, and its brine stream is difficult to dispose of. But, with good engineering designs and advanced technologies, these problems can be overcome. One approach is to use integrated design for efficient thermal desalination, by which the waste heat from power plants starts the treatment.
Desalination can also be integrated with wind and solar to mitigate its energy and carbon footprint. One of the challenges with wind and solar is that their output varies for different meteorological and astronomical conditions. The position of the sun in the sky, the prevailing wind, and cloud cover all affect wind farms and solar panels. This intermittency is a challenge for grid operators, but less so if intermittent wind sources can be matched with an intermittent load such as desalination. Water does not need to be treated in a perfectly continuous fashion, so the water treatment facility can be dialed up and down to match the availability of wind. The same idea can be used for sunlight. This approach makes particular sense in places like west Texas where sunshine is abundant, where it is very windy, and where there is practically an underground ocean of brackish groundwater. Using renewables together in this way to treat the water solves several problems at once.
Biological approaches may provide other useful models. For example, mangroves grow in seawater, producing freshwater with pressure-driven ultrafiltration.15 Enthusiasts have suggested that there might be a way to create mangrove plantations inside greenhouses or other capture systems, so that they could naturally produce freshwater at scale, without requiring massive input from fossil fuels. While this idea is appealing, it is akin to the idea of space-based solar power plants: both ideas have been around a long time, but both remain impractical for a whole variety of reasons related to cost, scale, and significant technical hurdles.
If the downsides of desalination—brine disposal, cost, and energy intensity—can be managed, then it is a promising source of freshwater for society, which can solve many water problems. However, as noted earlier, desalination can exacerbate energy problems, which invites these technical solutions (renewables, better design, etc.) to minimize impact.
If the challenges of desalination remain too vexing, then some communities can instead turn to harvesting water out of the sky. In particular, harvesting fog could be a ripe opportunity in certain parts of the world. There are some climates like northern Chile and San Francisco where freshwater is limited, but fog is abundant. In these locations, fog harvesters, which are mesh nets of tightly woven advanced fibers, can be erected vertically.16 As the fog passes through these nets, water droplets collect on the mesh and run to the bottom where they can be collected. These harvesters might be able to collect twelve liters (about three gallons) per square meter of net per day, which is enough to meet the needs of an individual. That means that in a place like Chile, millions of people could have their water needs just by collecting a few percent of the fog’s moisture. While those conditions do not necessarily apply in other parts of the world—and the chances of success from widespread implementation in Chile are still not known as it is in just proof-of-concept mode—every little bit helps.
In addition to switching the energy or water sources, it is also possible to implement advanced technologies that have enhanced performance. These include water-lean energy technologies, energy-lean water technologies, smart technologies, and distributed systems. Advanced technologies often have the drawback of requiring additional investment up front, in exchange for cost and resource savings downstream.
Switching to water-lean energy systems is particularly promising. Power plants can switch their wet-cooling systems to air-cooling or hybrid wet-dry cooling modes of operation. While that expense as a retrofit for existing power plants might not be cost-effective, for new power plants that might have trouble gaining access to cooling water, it can be a sensible approach to take. Because the heat capacity of air is one-fourth that of water, air-cooled systems must move four times as much air. That means the cooling systems need bigger fans and are much larger overall. Unfortunately, capital expenses scale with size, so the larger systems mean greater cost up front. At the same time, dry-cooling systems offer a performance disadvantage: power plants with dry cooling usually operate with an efficiency that is 2–10 percent lower than a similar system that uses wet cooling, depending on prevailing meteorological conditions.
In addition to dry cooling, there are also hybrid wet-dry systems. For example, some new designs from Johnson Controls use dry cooling in the winter, but wet cooling in the summer. In the winter, the air is cooler and usually the grid has sufficient power capacity available to meet demand. Because of the cooler air, the performance drawback from air cooling is not quite as bad as it would have been otherwise. And many power plants are looking to reduce their plumes of condensed vapor to reduce the visual pollution they cause. Switching to air cooling eliminates the plume and reduces annual water use.
In the summer, the performance cost of dry cooling is typically larger. At the same time, the summer is when the grid has less margin for error and so any performance cuts from power plants are felt more acutely. The hybrid system could be switched from air cooling, which works fine during the winter, to wet cooling, which boosts badly needed power output during the summer. In addition, plumes are not a problem in the summer as the hotter air temperatures prevent condensation of the evaporated water. In most places water availability is lower in the summer than the winter, so this arrangement would rely on saving up water during the winter months when air cooling is used so that the water is available for plant cooling in the summer.
The key tradeoff with dry-cooling systems is that they cause a persistent performance drag during normal operation, in exchange for performance resiliency during times of extreme drought or heat wave. Heat waves or droughts can force power plants with wet-cooling systems to draw down on their power output or shut off completely because of the risk of exceeding thermal pollution limits in the waterways or because of falling reservoir levels. Dry systems are less vulnerable to such problems. While the performance during a heat wave might be worse at a power plant, those with dry cooling are not subject to the thermal pollution limits because they do not dump heat into waterways. Because they don’t require water, the drought does not affect their performance. That means, while other power plants in the grid are turning down or off, the plants with dry cooling would be able to continue generating power. At the same time, power prices are usually higher when the grid is strained. The dry-cooled power plants that keep operating while the others dial back will make a tidy profit.
In a nutshell, that means power plants with dry cooling would trade a persistent small percentage power loss in exchange for having steady performance at the same time their competitors might not be able to operate at all. If droughts and heat waves become more prevalent, then dry cooling would be a more attractive option economically. It is somewhat like fire insurance for homes. Fires rarely burn down our homes, but when they do, they cause a lot of damage. The same idea could be used to describe a power plant’s vulnerability to being turned off from drought: it rarely happens, but when it does, the lost revenues are substantial. For the case with our homes, we pay approximately 1 percent of our home’s value each year to buy fire insurance just in case that rare fire happens. We have determined that it’s a lot easier to pay a predictable premium of $1,000–2,000 each year for insurance than to have the risk of paying $200,000–400,000 every fifty to one hundred years when a tragic fire happens. That math transfers over to power plants and their cooling: is it better to pay a 2 percent penalty in performance every year to avoid a 100 percent penalty that might happen only once every forty to sixty years? Our research at UT Austin suggests that it is worthwhile.17
However, switching the cooling system is expensive. In one case, state regulators required cooling towers to be installed at Oyster Creek, a 645-megawatt nuclear power plant in New Jersey, to mitigate environmental impact on Barnegat Bay. Estimates for the cost to convert the cooling systems ranged from $79 million to $801 million, which was prohibitively high. It ended up being cheaper for the operators to simply shut down the power plant rather than pay hundreds of millions of dollars for the cooling towers.18
While switching the cooling technology is an obvious way to reduce water use, switching the power cycle for the power plant also makes a difference. Coal plants use steam cycle designs with an overall efficiency of approximately 30–35 percent that do not compete well against more advanced combined cycle plants that have 40–60 percent efficiency, especially when the latter designs are coupled with cheap natural gas. Since the revolution of hydraulic fracturing, which accelerated starting in 2008, natural gas production in the United States grew quickly, pushing natural gas prices down from thirteen dollars per million Btu in the first decade of the twenty-first century to under three dollars per million Btu in the second decade. The century-long dominance of coal for electricity generation was threatened for the first time. For decades, coal has provided more than half of U.S. power generation, whereas natural gas provided about one fifth. However, in April 2012, when natural gas prices were about two dollars per million Btu, and overall electricity demand was relatively low, more electricity was generated by natural gas that month than from coal. That was the first time in U.S. history for such a phenomenon. Ever since the first coal plants came online, surpassing the hydropower capacity that had been built in the 1880s, coal has been the dominant power producer. While that month might have felt like a slight anomaly, the trend of decreasing power generation from coal and increasing output from natural gas is well under way and accelerated in 2015.
The increasing market share of those natural gas combined cycle plants comes primarily at the expense of traditional coal plants. This trend has several co-benefits: the newer natural gas plants are more efficient, produce fewer emissions, and require less water than the older coal plants. That means we can use plants that are clean and lean to replace those that are dirty and thirsty. While the water savings at the power plant are appealing, won’t the water used to produce the natural gas in the first place undo all those benefits? We asked the same question in my research group, and a gifted student named Emily Grubert answered it.19 She found that without a doubt, hydraulic fracturing for natural gas production requires more water per unit of energy than coal mining. However, she also found that the avoided water use at the power plant was much bigger than any increases at the point of fuel production. Those savings occur for three reasons. First, because the combined cycle plants are more efficient, they need less water for every unit of electricity produced. Second, the combined cycle is partially air-cooled, so even if the system had the same efficiency as coal, it would still save water. Third, because natural gas is much cleaner than coal, the water-intensive scrubbing systems to remove pollutants from flue gases could be avoided. Overall, the switch from a traditional coal plant to a new natural gas combined cycle can cut the life-cycle water intensity in half, in spite of the water requirements for fracking. This result was surprising to many, and I still get angry comments from people in the coal industry about that work.
Although this is good news about the life-cycle water intensity of natural gas—despite the water needs of the fracking itself—that doesn’t mean the water needs of fuel production should be ignored. The extractive industries can try new techniques that do not require freshwater, such as waterless fracking or use of effluent or saline water instead. For waterless fracking, there are a few different approaches. Some technologies use nitrogen-based solutions instead of water-based solutions, and other approaches use propane gels to fracture the formations.20 After injection into the shale, these gels evaporate into propane gas and escape out the well with the other gases that are being produced. The gaseous propane, which is a fuel, can be captured along with the other gases and used again in gel form or sold as a fuel. Although this idea has been demonstrated, some important risks of injecting flammable gases at high pressures deep underground still need to be managed.
Just as there are water-lean energy options, energy-lean water options can also be developed. Much of the energy intensity for water shows up in a few key places: water pumping, water treatment, and water heating. Water pumping is a pretty standard technology that has been around in a variety of forms for thousands of years. While pumps have improved significantly there is still more to do.21 Large water pumps require a lot of power. It is not unusual for a large pump to require nearly two megawatts of electrical power, which is the same amount of power that a massive wind turbine can generate. A pump that size could move water at a rate of more than fifty thousand gallons per minute. The efficiency of these pumps can be improved greatly.
Most pumps run at a constant speed. At the same time, approximately 75 percent of pumps are oversized, which means they are bigger than they need to be for the task at hand and are consuming much more energy than is needed.22 Incorporating variable speed drives (VSD) and variable frequency drives (VFD) allows for tighter control over pump operation, including the ability to tweak the flow rates to match the desired conditions. Most pumps are either off or on at full power. By using VSD or VFD to dial back on pump output to match what is actually needed, rather than just running at maximum power continually, much higher efficiency can be achieved: some reports indicate energy savings of 30–50 percent. This potential is particularly important for pumps that have variable-duty assignments—that is, they aren’t needed all the time. Ramping them up and down as they are needed saves a lot of energy compared with letting them run all the time. Changing their operation will also extend their lifetime and improve reliability. Switching to pumps with this design also saves a lot of money on energy requirements for moving the fluids around: it is reasonable to expect a payback within two years for this technology. These variable pumps can also be used to improve the power quality of the electrical grid, which can become distorted as we increase the number of electric vehicles and solar panels in our neighborhoods.23
Other opportunities are to improve the membranes that are used for treatment, especially for desalination. The membranes for desalination work by allowing water to pass through while leaving the salts behind. However, to use these membranes, the pressures of the water must be elevated above the osmotic pressures that occur from the salinity gradient. Better membranes could function at lower pressures, which would reduce the power requirements and therefore the energy consumption for the water pumps. Membranes also degrade from fouling. By designing the membranes with more advanced materials and more sophisticated structures, they will be better able to resist fouling, which means they will last longer and require less energy for manufacturing replacement parts and maintenance.
We can also use new approaches for water heating. Since nearly 4 percent of our annual energy consumption is just for heating water in our homes and businesses, improved water heating technologies represent a substantial opportunity to save energy.24 Much of this heating is done with electric water heaters. While electric water heaters are very efficient at the point of use, sometimes exceeding 90 percent efficiency, the power plants that operate them have 30–40 percent efficiency. Multiplying the efficiency of the power plant and the water heater together makes the life-cycle efficiency for conventional electric water heating about 27–36 percent overall, which is not that great. By contrast, natural gas water heaters with 60 percent efficiency at the point of use might seem worse compared to the 90 percent efficiency of electric heaters, but because they avoid the inefficient power plant, they are much better in end-to-end efficiency.
It is unfortunate that the EPA’s EnergyGuide labeling systems, which only identify end-use energy requirements instead of life-cycle energy requirements, have been nudging people away from gas water heaters toward electric heaters. If everyone in the United States who is currently using an electric water heater switched to a natural gas one, then we could save a nontrivial amount of energy per year. At the same time, for locations where the electricity is provided by clean sources—such as hydroelectric in Norway or the Pacific Northwest, or nuclear in France—switching from low-carbon electricity to relatively higher carbon natural gas water heaters would be a step in the wrong direction. When it comes to selecting the right water heating approach, technology and location matter.
We could also install point-of-use insta-hot water heaters, which heat the water on demand, usually with natural gas. This approach has several advantages. It is more efficient than electric water heating, and it heats water only when you need it, rather than traditional systems, which heat water around the clock even though it is needed just a few minutes or hours per day. Also, the homeowner never “runs out” of hot water, as it is continually generated, which is convenient when hosting guests and several showers and loads of laundry and dishes need to be supplied over a short span of time. Another advantage of the tankless water heaters is that they can be located next to the shower or sink. In many homes, the hot water heater is located on the opposite side of the house from the shower, which creates the undesirable situation that people let the water run in the bath for several minutes while waiting for the hot water to arrive. With hot water on demand right in the bathroom, this wasteful waiting game can be avoided. At the same time, tankless systems are smaller and more compact than large tanks, which saves space in the home. The downsides are their higher up-front cost—a standard tank water heater can cost $500 whereas a tankless one might cost $1,500—and the possibility that never running out of water will accidentally encourage people to take much longer showers or wash more laundry in hot water rather than cold water.
An even better option is to use low-grade temperature sources such as solar energy or waste heat in the house for water heating. Solar thermal systems for rooftop water heating are cost-effective and work well. Waste heat in the home can also be used. Our ovens, toasters, dryers, air conditioners, and refrigerators all generate waste heat. Waste heat recovery devices, which are small thermoelectric gadgets that convert temperature differences into electricity, are plagued by low efficiency, but as their costs come down and performance improves, they will become attractive options for houses. And, if we plumbed up our homes in a more efficient way, locating the sources of waste heat near where hot water is needed, then that waste heat could be used directly for water heating. The hot water pipe coming to our shower could pass by the back of the refrigerators, oven, air conditioner, or furnace before a tankless water heater in the bathroom does a final little boost of heating to bring it to the desired temperature. That approach would save energy in two ways. First, we would need less energy for water heating. Second, we would spend less energy on air-conditioning in hot climates to overcome the waste heat.
Another technical approach is to use distributed energy and water technologies, which might save water and energy, respectively. Large centralized power plants use a lot of water all in one spot and the large centralized water treatment plants use a lot of energy, also in one spot. By making them smaller, modular, and distributed around geographically, there is a chance that less water or energy will be needed. Or, even if they require a lot of water and energy, those requirements would be spread out rather than concentrated in a single location.
Distributed energy systems include rooftop solar photovoltaic panels that generate power for a home or building on-site. These panels do not require cooling water to operate. Other distributed energy systems might include microturbines operating on natural gas or propane, which are air-cooled. Fuel cell systems, which also do not require much water, are another possible solution.
Though the equipment costs of the distributed systems are generally two to three times higher per unit of electricity than conventional power plants, they offer some performance or environmental advantages. Solar photovoltaic panels are emissions-free, which is important for protecting air quality. And their production aligns reasonably well—though not perfectly—with peak demand in hot, sunny climates. Moreover, with sufficient energy storage for providing backup, solar panels can be used to keep the lights on and the air conditioner humming even during a power outage, on cloudy days, or at night. Batteries and flywheels can be used to store electricity, and chilled or hot water tanks can be used for storing thermal energy.
Natural gas fuel cells and microturbines can generate heat and power. The fuel cells are nominally cleaner than power plants as their low temperature operation avoids the formation of pollutants such as nitrogen oxides. Microturbines are also relatively clean, but not necessarily any cleaner than a natural gas combined cycle power plant. Their main performance advantage is that the gas grid, made up of gas pipes buried underground, tends to be less vulnerable to windstorms, trees, and critters than overhead power lines. Consequently, hospitals, city halls and other critical facilities look to these distributed systems as a backup to grid-tied power.
Because of the security and environmental advantages of the distributed energy systems, they are growing in popularity. They also bring along their low water requirements as a nice environmental co-benefit, whether it was desired or not.
Just as distributed energy systems can help avoid water needs, distributed water systems also can help avoid energy needs. In the current incarnation of the U.S. water system, most drinking and municipal water is treated at centralized large-scale locations, then pumped throughout the service area, including to far-flung suburbs.
On average the American consumer uses approximately 150 gallons per day of drinking water in their households. That water is typically pumped and treated centrally, then pumped again to distribute it to the homes. However, only a small fraction of that drinking water is actually used for drinking. The rest is used for washing, watering, and cooking. So another option is that only the drinking water is centrally treated, and the other water is harvested and prepared in a distributed rather than centralized way. Instead of water treatment facilities needing to procure and treat 150 gallons per person per day, they could do that just for 25–50 gallons per person per day. That means less energy will be required as there will be less water to treat and pump over long distances. The key here is that the water we need for showering, toilet flushing, and clothes washing does not need to meet the same standard as for drinking.
The other water that we use could be provided by distributed water harvesting and collection systems at the household or neighborhood scale. That water needs less treatment, and since it would be closer to the end-use it could avoid a lot of pumping costs. This solution makes sense only where there is local water like precipitation to harvest, so many desert communities might not be able to pursue this approach. And, just as for distributed energy systems, the distributed water systems might be more resilient compared with the concentrated systems that could be taken off-line by a targeted attack or unfortunate natural incident.
Centralized water treatment has distinct energy-efficiency benefits from economies of scale that can be achieved with larger systems. Therefore, distributed treatment of drinking water actually might increase the energy consumption per unit of water. However, those efficiency losses from smaller treatment volumes might be overcome by the energy savings from shorter pumping distances.
Putting these together, it is possible to imagine new concepts for the built environment in which homes harvest as much water and energy on-site as possible, relying on the centralized grid as little as possible. That means capturing and reusing graywater and rainwater on-site while also producing and reusing thermal energy on-site, both of which offer savings. On-site electricity generation avoids the water embedded in grid-tied power plants, and on-site water harvesting avoids some energy embedded in pipetied water treatment plants.
Another form of distributed water systems is on-site water treatment for the energy sector. The large volumes of water produced and used by the extractive industries represent an interesting opportunity to close the loop. Coal production generates water that gets pumped out of the mines, and hydraulic fracturing can generate millions of gallons of wastewater at each drilling pad.
Because the wastewater volumes are so large, they can end up being a constraint on production. And, trucking or piping such large volumes off to an industrial wastewater treatment plant can be prohibitively expensive. However, distributed on-site treatment using new processing technologies can save water and energy. If properly implemented, these mobile treatment systems reduce the contaminated wastewater stream volumes by an order of magnitude. Subsequently, very little water needs to be trucked away for additional treatment, and the cleaner water that is left behind can be used again. This distributed system avoids the energy of transporting so much water and enables additional energy production. In this case, the distributed system wins on multiple counts.
Among the many technologies, the suite of so-called smart technologies offers some hope for mitigating some of the worst problems in the energy and water sectors. Today’s dumb systems can waste water and energy without the wasters realizing it. Making matters worse, dumb systems are not resilient and are ultimately expensive. The idea of moving toward smart technologies, including ubiquitous sensing and smart meters for electricity, gas, and water to give more finely resolved information is appealing.
The most common type of electricity meter is a device that measures energy in kilowatt-hours through electromechanical induction. These meters were first demonstrated in the late 1800s. Remarkably, today’s meters operate on the same principle. The electrical current spins a metal disc at a rate proportional to the electrical power—this is the familiar rotating dial inside the glass bowl of conventional electricity meters. It rotates slowly except for when large appliances are operating, and the meter counts the rotations to track total usage.
These meters must be recorded manually by meter readers, which is inconvenient since the meters are often located behind a fence at the back of the house, above the thorn bush and protected by guard dogs. That our meter technology is so antiquated and requires an inefficient, labor-intensive process for meter reading is startling. Making matters worse, electricity meters slow down with time with a phenomenon known as “creep.” Cashstrapped consumers might appreciate these slow meters, because it means their bills are lower than they would have been otherwise. But it also means they—and the utilities sending them bills—are getting inaccurate information. Consequently, when new “smart” meters are installed, which probably have been recently calibrated, customers’ bills can go up because they are accurate for the first time in decades.
Water meters use a simple rotating vane technology that records cumulative usage and is also at least a century old. Similar to the electricity meters, they need to be read manually and slow down with time. Though their location, typically near the curb, is more convenient than the electricity meters, the process still requires the expense of rolling trucks to send out the meter readers. Natural gas meters are similar to water meters, but because gas is so combustible, gas meters in seismic zones have automatic shut-off valves to prevent explosive consequences after earthquakes.
The water, gas, and electricity meters share some of the same problems. One of the biggest shortcomings is that their measurements and billing are disaggregated from use and time. Monthly bills include consumption information that spans a thirty-day period. Processing, printing, and mailing those bills takes another one to two weeks, which means that by the time consumers actually read their bills, the consumption information they receive includes activity from as much as five to six weeks earlier. It’s pretty straightforward to assume that busy consumers might have trouble remembering what they did with their appliances forty days in the past. Water bills issued quarterly (not an unusual occurrence) exacerbate the problem even further. The complexity of the bills, cluttered as they are with separate taxes, fees, riders, and other costs not directly related to consumption, impairs the ability to interpret total usage. Few people have any idea how many kilowatt-hours of electricity, cubic feet of gas, or thousands of gallons of water they consume in a month.
Because the bill includes consumption information for the entire billing cycle, consumers are operating blind. The bills typically do not differentiate by time of day, date, season, household occupant, or appliance. That would be like shopping for groceries, but with no prices on any of the food items. With no price signal to steer our behavior, we would load up our carts with whatever looks appealing—steaks, specialty chocolates, and other high-priced items—leave the store, and take the groceries home, repeating that cycle twice weekly. We might even buy more than we need, throwing away the rest since for all we know it’s free. At the end of the month, the grocery store would send us a bill for all the food we had purchased. Imagine our sticker shock when we see the tally. If we had price information about each individual food item, then we could shop in a more intelligent way, buying only what we need, wasting less, and prioritizing the more affordable items.
This preposterous grocery story scenario is similar to our dumb electric bills. Without price signals on individual appliances, it is easy to waste electricity and to accrue expenses without realizing it. Consumers might understand the bill’s basic conclusions about their overall usage patterns, but might not know which particular appliances drive the consumption. If they knew how much energy their major appliances require, consumers might turn them off when unused or seek alternatives such as hanging clothes in the sun to dry instead of using the clothes dryer.
If we think the power sector is dumb, the water sector is even dumber. Water meters are often read quarterly, and in some municipalities such as Sacramento and Las Vegas there were no meters at all until recently, despite being in the middle of a desert. Wastewater is not measured, either. Rather, some utilities measure water use in the winter, assume all of this water is used for indoor purposes, as opposed to irrigation, and that all of that water makes its way down the drain, and then use that as the baseline estimate for the wastewater bill. That baseline is used for the rest of the year, whether irrigation is performed or not.
The idea that prices are the same for every appliance, every hour of every day of the year is astounding, as the rest of the supply and demand fundamentals of the market change every few seconds throughout the year. In the United States, electricity demand is higher in afternoons than nighttime and higher in summer than the winter. Water use is higher in the summer for irrigation than winter and higher during the day than night. Wind and water are both more abundant at times other than when demand for them is highest. Natural gas prices also have seasonal cycles based on demand for winter heating and summer power plant operation. However, for over a century our billing systems have not taken that information into account. Making matters even worse, some homes do not even have water meters installed; their bills include a flat fee based on the cost of infrastructure. These flat-fee bills actually encourage more consumption, since there is no price penalty for profligate or wasteful use of water.
This lack of information is particularly surprising given the revolution in the 1990s that dramatically reduced the costs of information technologies and opened up the pathway for ubiquitous sensing. It seems like the information revolution overtook every industry except for energy and water utilities. However, with the prospects for embedded information, the possibility to collect significantly more data about resource usage is tantalizingly close.
For electricity, gas, and water meters, it would be valuable to gain information about usage by time of use and the consumption of particular appliances. For water it would also be valuable to know the different types of water that are used: indoor versus outdoor, heated versus unheated, treated water versus graywater and blackwater, and piped water versus water collected on-site.
All this new information would be very useful for utilities and consumers. Consumers could track their own consumption and could also potentially track particular household members, which might be valuable for parents trying to convince their teenagers to take shorter showers. One friend of mine, Brewster McCracken, who is the CEO of Pecan Street, a nonprofit consortium conducting large-scale smart-grid and smart-water experiments, had a clever idea. Because his son has a propensity to take very long, hot showers, Brewster thought it would be a great idea to hang a timer in the shower that relayed price data from a smart meter. After some specified time limit, the readout would start counting down his son’s allowance, which would be taxed to pay for the extra hot water.
In addition to helping parents rear resource-conscious children, that information could be used to spot leaks or broken appliances. Utilities could use that information to respond more quickly to outages, to predict maintenance issues, and to cut costs by automating meter reading through telemetry rather than requiring employees to read every single meter manually. Rather than sending out hundreds of meter readers, a van could slowly drive through the neighborhood picking up meter signals along the way. Homeowners would benefit by fixing problems before they get worse, reducing the risk of fire in case of gas and electricity problems and before serious household damage occurs from water leaks.
The real-time information could be used to balance supply and demand, which is particularly relevant for the electricity markets. For on-site generators such as rooftop solar panels, the smarter meters could track how much power homes provide back to the grid to account for credits that would be due.
Smart meters and appliances will bring forth smart billing and smart pricing, too. In the United States, prices for electricity should be higher during summer afternoons, and lower in the middle of the night. In France, electricity prices should be higher in the evenings in winter when electrically heated homes cause demand to spike. Water prices should be higher in the dry seasons than wet seasons. With time-resolved metering, utilities could also implement time-of-use (TOU) pricing. These price tiers could have off- and on-peak price signals to shift demand across the hours and days. That also means regulators who use century-old business models to approve fixed prices will also have to become smart to allow utilities to shift to these newer pricing schemes. It is worth noting that most European countries, which many Americans decry as socialist, already have widespread time-of-day pricing so that they can exploit the power of markets to achieve efficiency. By contrast, capitalist America typically has fixed-price, infrastructure-based pricing. Leave it to those clever socialist Europeans to use market forces more effectively than capitalistic Americans.
The implementation of smart meters enables the installation of smart appliances, which might be used by utilities for grid balancing. Nonessential appliances such as pool pumps or hot water heaters could potentially be turned off automatically during peak loads or high price times of day to save consumers money. There are even some designs for smart clothes dryers that keep the tumbler rotating but turn off the heating element periodically when the grid needs to reduce demand. In France, there are more than 13 million smart electric water heater units installed. They have a peak demand at night in the winter of eight gigawatts, which is equivalent to the output from seven nuclear power plants. By remotely turning them down when they are not needed, three gigawatts of consumption can be avoided.25
These new technologies also democratize the infrastructures, allowing third-party vendors into the system who will sell services that help consumers reduce their expenditures. These energy service companies (ESCOs) help instrument and manage a building especially for the commercial sector, reducing consumption and saving customers money. The ESCOs earn revenue based on a portion of the savings—the more they save their customers, the more money the ESCOs earn. But such business models are hard to implement with the existing dumb systems. For the residential sector, opening up the data streams means consumers might be able to buy a clear, digital readout to install in their kitchen with real-time, appliance-specific, and cumulative consumption information—much better than the slowly spinning analog dial that is outside at the back of the house and hard to read anyway.
The smart systems still have downsides, and we would be wise to prepare for them. There are the security challenges: to security experts smart devices look like entry points into our critical infrastructures, making them vulnerable to cyberattacks. This issue is real and worthy of further consideration. However, one counterargument is that a web of smart devices coupled with distributed energy and water systems would be inherently more resilient and able to respond more quickly in the event an attack actually occurs. Rather than providing a target of just a thousand power plants and thousand water plants for the existing, centralized system, the smart, distributed system would have millions of different devices, making it harder to take them all off-line in a single fell swoop.
Another disadvantage is the looming burden of “big data.” According to humorous observers, big data is like teen sex: everyone is talking about it, everyone thinks everyone else is doing it, but in truth we are all just clumsily fumbling around in the dark trying to figure out how to make the different pieces go together. Today’s dumb system has the advantage of including very little data, which means there is not much information to collect, store, archive, or retrieve. Conventional meters have two data points for a billing cycle: one data point at the beginning of the month, and another data point one month later. The total consumption is simply the difference of those two points. A smart system will have more frequent readings: with a fifteen-minute interval between readings—which is typical—meters will produce about three thousand meter readings per month. But, utilities, working with decades-old software and computing systems, are often ill-prepared for such a transition to the twenty-first century. They often do not have the skilled personnel, the data, the computers, or the cultural mindset to use these datasets, much less make them available to consumers.
For one case study, Austin Energy, a municipal utility on whose governance board I served for five years, completed a rollout of smart meters to more than 300,000 customers from 2008 to 2010. Austin Energy is often considered one of the nation’s leading and most forward-looking utilities, and so it is not surprising that they were one of the first major municipalities to complete the installation of so many smart meters. The whole effort cost a little over $150 per meter, or about $50 million in total. After quickly installing the meters they discovered that their antiquated data systems, not to mention their personnel in their customer service billing divisions—simply were unprepared for such an event. The billing systems were not upgraded until more than two years later, in late 2012, at a surprising cost of an additional, unexpected $50 million. Handling the data cost just as much money as installing the systems themselves. Big data is liberating and enabling for the consumers and utilities, but is also expensive and cumbersome to manage.
In some ways, the smart revolution is an allegory for everything else about these infrastructures: it is a solution to one set of problems that introduces a new set of problems. And so the cycle will begin again.
Some of the smart grid benefits for electricity might also be relevant for the world of smart water. My good friend Amy Hardberger is a water lawyer and a collaborator for some of the research discussed in this book. She is an active environmentalist who practices what she preaches, attentive to her resource consumption and aware of the impacts to the environment.
One day in the late 2000s, while working in her yard, she discovered her water meter buried a few feet underground. She naturally wondered how her water bills were generated if the meter was located several feet underground. She called to inquire about how the water utility determined the amount of her bill each month.
The water utility replied that a meter reader goes by each house to determine the amount of water that had been consumed, which sets the bill. While that answer would have been true in many corners of the United States, Hardberger laughed, knowing that the answer was wrong, as her meter had been securely buried underground. Presumably the meter reader had been making up numbers for years to make up for his or her inability to actually read the meter as that would have required a serious digging exercise. Knowing that a high bill would raise concerns, the reader probably cleverly skewed the numbers low, figuring that a low bill would not inspire complaints by the homeowner. That Hardberger was a prudent water user was coincidental: for her, low bills would have been appropriate, as she consciously kept her water use to a minimum.
This anecdote reveals just how dumb our water infrastructure can be. But the power sector is also considered dumb, as very little information is embedded with the end-use consumption. Many consumers such as tenants in apartment buildings have absolutely no idea how much electricity they consume, if the utility charges are included in their rent. In many cases, individual apartments or condos do not have independent meters, as all the consumption is aggregated into a single meter for the entire building. Further, in many municipalities, that bill often aggregates several services, including water, wastewater, and trash disposal. That means customers don’t have good information about their consumption, but it also means that many leaks and losses go undetected.
I have my own experience with dumb meters, which is slightly embarrassing because I try to be attentive to energy and water matters. My house has very hard water that causes buildup in the pipes and tends to be damaging over time. In mid-October 2010, that buildup caused a break in a hot water pipe in our home’s concrete foundation, but because of a dumb water meter, a dumb electricity meter, and a dumb homeowner—me—I did not figure out that we had a leak for two and a half months.
It started when my wife and I noticed that there was a spot in our concrete floor that was a little warmer than normal. We didn’t really know what to make of it. Our electricity and water bills came a few weeks later and I didn’t notice any variability beyond the normal range. To be honest, I was not looking at the bills with any more scrutiny than normal, but even if I had, since bills change month to month anyway, it’s not clear what I would have seen.
As the weeks rolled on, the warm spot in the floor didn’t go away. Our water usage was about 50 percent higher than normal, but since most of a water bill is composed of fixed monthly costs and very little of the bill depends on water consumption, the total amount of the bill didn’t change much. Our electricity bill didn’t change, either. While we have a solar thermal system for our water heating, because the water was being used continually, the electric backup for the heater would have been triggered. We were undoubtedly spending more electricity heating water, but since it was in the fall, our use of air-conditioning was dropping. Despite the hot water leak and the additional electricity consumption for water heating, our electricity bill actually dropped overall.
Finally, yet another month later, the spot in the floor was getting progressively warmer, a crack emerged in the floor by the back of the house due to shifting soils from extra water, and our third bill arrived—a full two and half months after we first noticed the warm spot. By this point we could hear water rushing. I hate to admit how slow we were to figure out what was happening, but it finally dawned on us from all those separate points of evidence that there was a potentially expensive and damaging hot water leak inside our concrete slab.
We called the plumber and discovered we were lucky. First, the slab wasn’t damaged, which is remarkable. Repairing a damaged slab can easily cost tens of thousands of dollars. Second, the pipe could be fixed through a bypass in the wall, which only required the removal of some sheetrock rather than drilling or cutting into the slab, saving us many thousands of dollars.
While smarter homeowners could have avoided this risk—the irony of an energy-water nexus researcher getting hit by an energy-water nexus failure without noticing is worthy of some sort of parody—a smarter system could have spared that wasted water and electricity and avoided the risk of expensive damage and repairs. A smart water system could have alerted us that flows out of the hot water heater were much higher than normal and were occurring around the clock, rather than just when hot water appliances and fixtures were being used. A smart electricity system could have alerted us that the consumption for the hot water heater was much higher and steadier than normal. Smart meters would have given us data every fifteen minutes instead of every month. Thus, instead of needing two and a half months to get three data points about our use, we could have been alerted within a few hours.
Such a smart system would have been very advantageous. But, like most Americans, we did not have such a system. Scaling that idea larger, the utilities would benefit from having sensors and meters that automatically alert them to power outages and leaks. Today they rely on people to call the utility when there is an outage. In those cases, based on the location of who calls in, they can identify the affected area and search for the problem by sending crews out with trucks and flashlights. With a smart system, the utility would know the exact location of the break, reducing outage times dramatically.
While the fancy bells and whistles of smart water and advanced technologies are appealing, some low-tech solutions can also be very effective. One of those ideas is the WaterWheel, which is a round container that holds fifty liters of water and can be rolled like a wheel.26 For poor people who do not have the energy for piped water and have to collect water manually—namely, women—the wheeled container means they can roll the water from the well to their home rather than carrying it on their heads, reducing the burden. While this is not quite as convenient as a modern piped system, it is a step in the right direction.
We can also try cross-sectoral problem solving. Although the water sector’s problems can become the energy sector’s problems and vice versa, the corollary is also true: each sector can integrate solutions that mitigate problems in the other. We can use the water sector to produce energy and the energy sector to produce water.
One useful example is the approach of turning wastewater treatment facilities into producers of energy rather than consumers of energy. A nontrivial amount of energy is required for wastewater treatment facilities. That energy goes for a variety of purposes such as pumping, filtering, stirring, and ultraviolet irradiation. Consequently, energy expenses are the primary operational costs for the treatment plants. As treatment standards get stricter, the energy requirements typically increase.
However, wastewater treatment facilities also circulate large volumes of water that have a significant fraction of organic content. If the organicrich wastewater sludge is sent through anaerobic digesters, then the decomposition of the sludge would produce biogas, a mixture of methane and carbon dioxide. This process also produces a solid digestate that can be used as a fertilizer. Anaerobic digestion is not that controversial as a treatment approach, as it is already implemented around the world. But unfortunately, much of the biogas that is generated is either flared or vented: few facilities actually put the biogas to work.
Wello’s WaterWheel is one low-tech innovation—the water vessel is also a wheel—that will reduce the burden of manually fetching water. [Photo courtesy of Wello]
Facilities that capture and use the biogas for process heating or on-site electricity generation will reduce their energy bills, though there are additional capital costs for the digester equipment if the utility did not already own them. It is even possible for many plants, especially those with larger flows that have more potential for generating biogas, to become nearly energy self-sufficient.27
In Austin, the use of digesters produces solid waste materials that are then mixed with plant trimmings to form a valuable soil amendment known as Dillo Dirt. “Dillo” is short for “armadillo,” which is a prehistoric-looking creature native to central Texas. The city sells the soil amendment to landscapers, farmers, and home gardeners. Doing so helps close the loop, turning the waste stream into a valuable commodity, while at the same time generating revenues for the wastewater treatment facility. The sludge-to-biogas-to-fertilizer approach serves two purposes: saving money and saving energy. Because fertilizers are energy intensive to manufacture—they are typically made by converting natural gas into ammonia—each pound of Dillo Dirt fertilizer produced from wastewater saves energy. That means wastewater treatment plants can go from consuming energy for their operations toward producing energy in the form of biogas and saving energy elsewhere.
While Dillo Dirt is a good news story, it is not without its controversy. Two of Austin’s gems converged in a messy story in October 2009. Austin City Limits is a live music show that has run continuously for decades, making it one of public television’s most successful programs of all time. It is also an Austin landmark of sorts, as it affirms Austin’s self-declared designation as the live music capital of the world. In addition to the television show, filmed before a live studio audience, the Austin City Limits festival is attended by nearly a half million live-music lovers over several days. It takes place in the fall at Zilker Park, a large and iconic urban park along the south shore of the Colorado River that winds through downtown.
The fall weather in Austin is unpredictable, varying from hot to cold, wet to dry. After several years in a row of dry weather, Zilker Park’s lush green fields turned to dust, causing massive dust clouds for the 2008 festival, which took away from the normally joyous atmosphere. To prevent that problem from happening again, the festival organizers and the city of Austin resurfaced Zilker Park’s fields in advance of the festival in 2009. In doing so, they amended the soils with Dillo Dirt. As fate would have it, that year would be remarkably wet, with epic rainstorms occurring during the festival. The formerly dry, dusty fields turned into boggy fields of gooey mud several inches thick. People were losing entire shoes and other garments and personal items in the quicksand-like fields. News spread quickly that the soils and mud were laced with Dillo Dirt. Festive partygoers who reveled in the idea of frolicking in the mud in some sort of mass remembrance of Woodstock decades earlier quickly became disgusted when they realized that they were shin-deep in human waste. Treated human waste, to be sure, but human waste nevertheless. The initial outcry, even for Austin, was notable. No one died and Dillo Dirt was declared safe by public health authorities, but this episode reveals that even in environmentally conscious Austin, recycling our wastes for useful purposes can still hit some roadblocks.
Just as the water sector can be used to generate energy, if designed the right way, the energy sector can transform from being a water consumer to a water provider. Some of the water that oil and gas operations produce is mildly brackish and could be used for industrial applications such as power plant cooling. Or the produced water could be collected and used again at neighboring sites. If combined with distributed wastewater treatment technologies, the oil and gas sector could even generate freshwater on the drilling pad. Scaling up this idea, oil and gas companies might someday become oil, gas, and water companies. Instead of spending money to get water, they will earn money to provide water. The oilfield service companies—Halliburton, Schlumberger, and National Oilwell Varco—are already thinking about this, as water management is one of the biggest headaches at the well pad.
One opportunity would solve three problems at once. The shale revolution has created a remarkable upswing in domestic oil and gas production. It has also produced three significant environmental drawbacks: increases in demand for freshwater for hydraulic fracturing, produced water with high levels of solids and undesirable constituents, and flaring of natural gas. Gas flaring is particularly common in places like the Bakken Shale in North Dakota and the Eagle Ford Shale in south Texas, which produce a lot of gas along with the oil, but lack sufficient gas pipelines to move the gas to market. Gas flaring in Texas more than tripled between 2010 and 2014, and about a third of the natural gas pulled out of the ground in North Dakota is flared. Flared natural gas is an environmental challenge because it has all the pollution of combusting fuels without harnessing useful services. The water competition for fracking and produced water are also challenging for all the reasons discussed previously. But by putting together the two waste streams—flared gas and produced water—a new source of water can be supplied, reducing competition with other sources. Flaring is particularly prevalent during the first few weeks of a well’s completion. That is also when the wastewater flow rates are highest and the levels of dissolved solids are lower. Instead of being flared, the gas can be used as energy to treat the water, turning the two waste streams into a useful commodity of water that is clean enough to be used again. In Texas, we found that if just the gas from the first ten days of flaring was used to treat the wastewater, it would increase statewide water supply by 1–2.5 percent.28 Since many of the shale basins are in water-stressed areas, this solution would be particularly useful for mitigating water strain from increased shale production.
The power sector can also be used to generate water by coupling power plants with desalination systems. This idea was flagged earlier with the possible switching to saline or brackish sources, which can be performed by coupling the water treatment system to a wind or solar power plant. Doing so solves several problems at once. Wind and solar farms are plagued by intermittency, as they only work when the astronomical and meteorological conditions are favorable. This intermittency causes problems for grid management and is one of the most important downsides of those renewable sources.
This intermittency is both predictable—the sun not shining at night, for example—and unpredictable, such as that due to sudden weather changes. On the other hand, desalination of brackish and saline sources is very energy intensive and therefore carbon intensive because of its reliance on today’s fuel mix. Integrating the two allows them to help mitigate each other’s problems. The water treatment process itself can be operated in an intermittent way to match when the wind or sun are available. That is, instead of changing the power plant’s supply up and down to match the demand from the user, the demand can be turned up and down to match the supply. As wind and solar vary hour by hour, the desalination plant can follow it, consuming the power when it is available and idling itself when power output is low. Because wind and solar are low-carbon sources, they help mitigate the carbon emissions from desalination that is powered from the conventional grid.
In what can only be described as a cruel joke by Mother Nature, some of the world’s major solar-rich deserts overlay abundant brackish groundwater, as in northern Africa. There are also abundant solar and wind resources in desert areas of the United States, such as New Mexico and Texas, where significant resources of brackish water aquifers are located. In the southwestern United States, the co-location of wind, sun, and brackish water might make desalination a more attractive option economically and environmentally. And, there are locations where the brackish aquifers are fairly shallow, the water is not very salty, and wind or solar resources are abundant. In those locations, it is more profitable to use the renewable energy to generate freshwater than to make electricity. Such a coupled system takes two low-value products—brackish water and intermittent renewables—and turns them into a high-value product (treated drinking water).
Research performed by my students found that in areas with a lot of wind and solar resources, large volumes of shallow and mildly brackish groundwater, and high local water prices, an integrated system may significantly improve the supply of water and electricity and is potentially more profitable than a standalone power plant.29 An integrated facility would require a large up-front capital investment. But, then it would be more flexible, as it could produce electricity and water, and it would be more efficient overall. Plant operators would benefit by hedging the power and water markets, selling whichever commodity is most profitable at that particular moment. An integrated plant would sell water when water prices are high and would sell electricity when electricity prices are high. It could easily store water when conditions are mediocre for its sale. Storing desalinated water could act as a proxy for energy storage. Notably, it is a lot cheaper and easier to store water than it is to store electricity. Instead of expensive lithium-ion batteries, for example, you can simply dig reservoirs or use holding tanks.
Because groundwater is typically cooler than surface conditions in warmer climates, it could be used to cool solar panels. While solar panels do not require cooling, doing so improves their efficiency. In the process of cooling the solar panels, the brackish water is heated, which improves its membrane throughput and recovery during the desalination process. It is a win-win scenario, with both water and electricity being produced with higher efficiency.30
In addition to wind and solar providing electricity, they can also provide direct inputs to drive the process. Windmills, instead of generating electricity, could provide direct mechanical power to operate the pumps that push the brackish water through membranes. And solar systems, instead of generating electricity, could generate the heat that is used to boil the brackish water. The energy requirements of the first approach depend on the salinity of the water, and the second approach depends on how hot the water feed is.
One of my students conducted a global examination of where solarbased desalination makes sense and could potentially be done sustainably.31 She used several criteria: locations where freshwater is scarce, urban populations exceed one million people, it is sunny, and the water is warm but not too salty. The thinking is that people would not be willing to endure the expense of a desalination system unless water is scarce, and that only large municipal areas could accumulate the necessary capital to build the system. Once in place, those systems are more efficient if the water is warm, which helps it flow through the membranes; the water isn’t too salty, which reduces the energy required for desalting; and sunshine is abundant. This research determined that there are indeed places throughout the tropics where water and radiation conditions are well matched for solar-powered desalination: the Bay of Bengal and other tropical locations with large cities near the coast met the criteria. The same kind of analysis could be done for wind-powered desalination, identifying water-stressed cities near the coast where wind is abundant and the water isn’t too salty or cold.
Another approach is to use the waste heat from the conventional power sector to perform desalination. This is the approach used in Abu Dhabi, where desalination plants are coupled to power plants. The power plant runs on natural gas, and the waste heat boils an incoming stream of seawater. This integration makes perfect sense for a place like Abu Dhabi, which is energy rich and water poor: trading energy for water is a very rational thing to do. And using the waste heat for the desalination is an efficient design from an engineering perspective as it saves significant energy for producing freshwater.
One surprising outcome from Abu Dhabi’s arrangement is that it produces extra water in the summer and waste electricity in the winter.32 In the summer, when desert temperatures are soaring, the electricity demand for air-conditioning is very high. Because the water production is tied to electricity production, as more power is generated, water is produced, too. High electricity demand in the summer means excess water production. Unexpectedly, there is more water available in the summer than the winter when power demand is relatively lower.
As there is no place to store it with the existing infrastructure, that water is used for seemingly profligate purposes such as irrigating golf courses and growing crops that are not native to the desert. Maintaining these golf courses and crops keeps the need for freshwater high in the winter. As a result, the power plants are turned on just to make the heat to desalinate water to meet this demand.
From an engineering perspective, the integration of power production and freshwater treatment is nominally a good idea that yields performance improvements. But, including the human element, this coupling causes wasted water in the summer (because of excess electricity consumption) and wasted electricity in the winter (because of excess water consumption).
That anecdote is a good reminder that taking a holistic view for resource planning is the critical missing piece. Systems-level thinking and integrated designs can improve efficiency, reliability, cost, and robustness. Unfortunately, political roadblocks and isolated decision-making often make those approaches difficult to implement. Those technical solutions still are not enough, as we hit human barriers with bad policies, poorly designed markets, and cultural indifference. We need nontechnical solutions, too.