Water's getting a lot of attention these days.
The original urban water system started in Ancient Rome, where pieces of aqueducts can still be seen. But for modern civilization? How we get our water is usually out of sight, out of mind.
"But actually, there's a remarkable hidden world bringing water into our homes, treating it before it goes back out into our environment, and providing us with all the water we can ever want," says University of California Berkeley professor David Sedlak. His book "Water 4.0" looks at how civilizations have dealt with their water problems.
"It's part of the same story about water infrastructure -- no longer up to the challenges that nature's throwing at it," says Sedlak.
For example, the city of Perth in Australia used seawater to solve their water crisis:
Sedlak says he's surprised that overhauling existing water systems happens in a relatively short period of time. And that investing in water systems now can save money throughout the next century.
"You don't appreciate water until it's not there," says Sedlak. "What we're seeing is precisely what the climate change models predict -- the wet places are going to get wetter, and the dry places are going to get drier."