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.

With 20 percent of the world’s population but just 7 percent of its available freshwater, China faces serious water shortages as its economy booms and urbanization increases. The government is planning massive water diversion projects, but environmentalists say conservation — especially in the wasteful agricultural sector — is the key.

A dispute between Egypt and upstream African nations has brought to the fore a long-standing controversy over who has rights to the waters of the Nile. The outcome could have profound consequences for the ecological health of the river and for one of the world’s largest tropical wetlands.

Hydro fracturing is a profitable method of natural gas extraction that uses large quantities of water and chemicals to free gas from underground rock formations. But New York City’s concerns that the practice would threaten its water supply have slowed a juggernaut that has been sweeping across parts of the northeastern United States.

As governments, businesses, and homeowners plan for the future, they should assume that the world’s oceans will rise by at least two meters — roughly seven feet — this century. But far too few agencies or individuals are preparing for the inevitable increase in sea level that will take place as polar ice sheets melt.

Bolivia accounts for a tiny fraction of global greenhouse gas emissions. But it will soon be paying a disproportionately high price for a major consequence of global warming: the rapid loss of glaciers and a subsequent decline in vital water supplies.

The coal industry, political leaders, and some environmentalists have high hopes for the concept of carbon sequestration, which takes carbon dioxide emissions from coal plants and buries them underground. But so far, this new technology does not live up to the hype.