[00:09] In rural areas of the American Midwest, windmills like this one regularly pump groundwater for irrigation and drinking water.

[00:18] Groundwater is abundant, but it's also one of the most exploited of Earth's natural resources.

[00:23] On the other hand, groundwater is not infinitely renewable. When it is pumped out of the ground faster than it is replenished, users are living on borrowed time.

[00:34] Most groundwater is found in subterranean fossil reservoirs called aquifers. And because rates to recharge aquifers is slow, they are not considered renewable.

[00:43] When aquifers are pumped faster than they can be recharged, a situation called overdraft, they are useless as reliable water sources.

[00:51] A good example of aquifer overdraft is the Ogallala aquifer, Earth's largest aquifer. In some places, the Ogallala aquifer is dropping more than six feet a year.

[01:01] What will happen when the Ogallala aquifer finally runs dry? Farms, industries and residents that depend on the Ogallala will face dry wells. The region's beef industry and supporting economy would be devastated.

[01:14] Overuse and degradation of the world's groundwater is among the serious environmental challenges facing human populations in the coming decades.

[01:23] To learn more about Our Changing Planet, visit us on the web at www.umac.org/ocp.