America’s long complacency about its water supply is being eroded not just by crises like Flint, Michigan’s lead-poisoned pipes, but by a growing realization that, as clean water becomes scarcer, especially in the West, it can’t remain so cheap. Just 2.5 percent of the world’s water is fresh water that is actually available, and pure enough to drink. Right now, water technologists are hard at work on two separate challenges: squeezing more drinkable water from the oceans of water already out there and devising new ways to use — and waste — less of the water we already have. Here’s a sampling of new technologies that promise to change the future of water.