1854

Water Treatment

John Snow (1813–1858)

Millions of people wake up every morning, and one of the very first things they need is water. In America, consumption averages 80 gallons (300 liters) per person per day. Every municipality across the country has engineers who work to make that possible at the water treatment plant.

In many municipalities, the water starts in a reservoir or man-made lake. The municipality taps into the lake with a large inlet pipe, and the water contains two contaminants that need to be removed: 1) particles like soil, leaves, fish waste, etc., and 2) various types of bacteria and parasites. Thanks to English physician John Snow’s study of the 1854 cholera outbreak, we now know that in order to prevent illness, we need to remove these contaminants. A quick burst of chlorine at the intake will kill the algae and bacteria and turn them into particles. The next step is to remove all the debris.

One common approach: add alum and other coagulants. Once in the water, alum molecules have a charge that attracts the particles. This process is called flocculation and produces flocs.

Engineers create large, still, settling areas for the water to pass through. This gives the flocs time to sink to the bottom. Next the water flows though large sand filters, like the sand filters found in swimming pools but at a much larger scale. These filters will catch any remaining particles, any remaining parasites, and many of the remaining bacteria. The final step is sterilization. Three techniques have become popular: chlorine, ozone, and ultraviolet light. Some people do not like the taste of chlorine, but the advantage is that it stays in the water as it moves through the pipes and it is easy to filter out once it arrives in the home. The study of water treatment has lead to other ways of making potable water out of potentially contaminated source material, such as desalination.

SEE ALSO Modern Sewer System (1859), Desalination (1959).

A pool for water treatment is pictured here.