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.

For decades, deadly outbreaks of cholera were attributed to the spread of disease through poor sanitation. But recent research demonstrates how closely cholera is tied to environmental and hydrological factors and to weather patterns — all of which may lead to more frequent cholera outbreaks as the world warms.

The inland Niger delta of Mali is a unique wetland ecosystem that supports a million farmers, fishermen, and herders and a rich diversity of wildlife. But now, the country’s president and Libyan leader Moammar Gaddafi have begun a major agricultural project that will divert much of the river’s water and put the delta’s future at risk.

For years, a chemical plant in the Chinese village of Qiugang had polluted the river, poisoned the drinking water, and fouled the air — until residents decided to take a stand. The Warriors of Qiugang, a Yale Environment 360 video co-produced by Ruby Yang and Thomas Lennon, tells the story of the villagers’ determined efforts to stop the pollution.