Vampires Vs. Aliens, Book One

Their existence depends on stealing a precious fluid humans need to stay alive: for vampires, it's blood; for the aliens, it's water. But if the aliens succeed in draining the Earth's oceans, all humans and animals on the planet will perish taking with them the sole source of blood the vampires require to survive. Now the vampires must wage a secret war against the invaders while keeping hidden their own existence from the humans, just as the aliens don't wish humanity to learn of their invasion already underway.