Three hundred and thirty-two million Americans take for granted the presence of an abundant, safe, clean water supply. If ever it falters, as in Flint, Michigan in 2014, it provokes a political crisis. Even in the desert states of the American West, great cities like Los Angeles, Phoenix, and Salt Lake City have plenty to drink, while millions of gallons are left over for intensive irrigation farming on once-arid lands. The American water supply, like everything else, has a history. It features ingenious engineers working out how to control, regulate, store, and purify billions of gallons. They were so successful that for nearly a hundred years now we have stopped appreciating their phenomenal achievement. But the current drought in the American West is drawing renewed attention to the threat of water shortages, making this a good moment for us to think about how we got to this point, as well as our prospects for the future.