Nature has a review of a new book on worldwide groundwater depletion. Remember, we are losing glaciers and snowpack in important food-growing regions at the same time it appears we are seeing more extreme and long-lasting droughts. Groundwater overpumping seems to be a wound we are inflicting on ourselves at the same time we are dealing with these external threats.

Some 95% of unfrozen fresh water resides unsung and underground, dimly visible at the bottom of a well or gushing from a pump. Big cities such as Buenos Aires and entire countries, including Germany, depend hugely on groundwater. About 70% of it goes into irrigation, accounting for more than half of irrigated agriculture — which in turn provides nearly half of the global food basket. In large parts of India, groundwater is egregiously overdrawn. And everywhere, aquifers are poorly measured and managed. As a result, no scientific consensus exists on the details of this vast and vital source of fresh water — although there is consensus on the fact that we face a worldwide problem.

In High and Dry, hydrologist William Alley and science writer Rosemary Alley encapsulate the crisis in a description of the US High Plains Aquifer, which spans eight states from South Dakota to Texas. “This virtual ocean of groundwater, which accumulated over thousands of years, is being used up in decades,” they write. In three ways, the book provides a deep and broad understanding of groundwater use and abuse, mostly in the United States but with some international scope…

The well could empty for millions more. The United Nations Development Programme notes that, in 2011, more than 40 countries experienced water stress; of those, 10 have nearly depleted their renewable freshwater supply. By 2050, one in four people globally may be hit by periodic shortages. The near future could see refugee numbers swell, to include more people without water.