Today, an estimated 3.6 billion people live in places where access to water isn’t guaranteed for at least one month every year, according to a UN report released in 2018. This problem is not going to get better in the future: The world’s population is expected to grow by another 3 billion people by 2050, increasing water demand by a third. At the same time, climate change will have dried up some watersheds and caused contamination by flooding in others. The combination of population growth and diminished water access means that the number of people who don’t have a reliable water supply for at least a month per year could grow to as much as 5.7 billion.
But humans exist on a very short leash. A person can only last around three days without drinking water. In our very recent past, humans could afford to think of water as more or less a constant. Yes, drought hit, and other years brought flood, but eventually things returned to normal. But the next several decades (and indeed the decade we are currently living through) are a departure from the luxury of normal; water is undergoing a regime change. Drying reservoirs aren’t going to fill back up with the consistency we’ve come to count on. Water security will be one of the principal struggles of the modern era.
Wasting used water—by flushing it down the toilet or sink, to be discharged into rivers and into undrinkable oceans—might be inconceivably irresponsible. A closed-loop water system, in which we drink water, expel it, treat it and drink it again, might be the future. Indeed, in a handful of places around the world, it already is.