So there is a cycle of renewal at work, but this delicate cycle depends on a lot of complex factors, including rainfall, soil, weather, and river flows— all of which humans have impacted, to our own misfortune. We’ve cut down half the planet’s forests, so there’s less soil and earth to stop rainfall from going directly to the rivers. We’ve dammed up the rivers, which interrupts their complex ecosystems— in the U.S., only 2 percent of the rivers aren’t dammed— and some rivers, like the Colorado and Rio Grande, hardly even make it to the sea. So while the earth can’t run out of water— humans can run out of freshwater, and we are. For us, water is a finite resource.

And for many people in the world, access to this finite resource is a matter of survival. Diseases like cholera and dysentery are caused by unsafe water, and the number one cause of infant death worldwide is unsanitary water. In places like Haiti and Gambia, people only have 3 liters of water per day— here, in the U.S., we use 500 liters per day. The average toilet made before the mid-1990s uses 23 liters in a single flush. It is important to understand this vast inequality as we explore the issue of water in our world. As Peter Glieck puts it, “It’s a human tragedy, which could explode into a human bloodbath.”3 For us, the water crisis is coming; for the 2.2 billion people that live below a minimum level of water need,* it’s already here.

* This 50-liter requirement of minimum need is based on the following: 5L for drinking, 10L for cooking, 15L for bathing, and 20L for sanitation. Obviously, many people get much less than this.