Since pre-Islamic times, Oman’s water systems known as aflaj have brought water from the mountains and made the desert bloom. But now, unregulated pumping of groundwater is depleting aquifers and causing the long-reliable channels to run dry.

A potential answer to California’s severe water shortages is groundwater banking, which involves creating incentives for municipalities, farmers, and other water users to percolate water down into sub-surface aquifers for later use.

Kenya’s high-elevation forests are the source for most of the water on which the drought-plagued nation depends. Now, after decades of government-abetted abuse of these regions, a new conservation strategy of working with local communities is showing signs of success.

Urban stormwater runoff is a serious problem, overloading sewage treatment plants and polluting waterways. Now, various U.S. cities are creating innovative green infrastructure — such as rain gardens and roadside plantings — that mimics the way nature collects and cleanses water.