Meeting water needs is a primary goal in our crowded world. There have been successes. For example, 2 billion people received clean drinking water between 1990 and 2012. Still the water needs for many people in developing countries are very serious.
Another success lies in domestic freshwater consumption. Americans use less freshwater today than in 1980, even with an increase in population. This is due to increased efficiency and better planning and allocation of resources.
70% of water use worldwide is used for irrigation, followed by 20% for industry, and 10% for human use. In the United States, 20% of domestic water comes from groundwater and 80% from surface waters such as lakes, reservoirs and rivers. The United States is fortunately rich in water supplies.
In other areas of the world, water is more scarce or hard to come by. As high as 1.1 billion people only have access to wastewater and not purified water. Contaminated water supplies account for deaths of more than 1.6 million people per year, of which 90% are children.
Groundwater is the large, unseen storage of water that accumulated slowly in porous rock over millennia. 99% of all liquid freshwater is in underground aquifers.
It takes almost a century or longer to recharge these aquifers. Hence, they are considered nonrenewable.
The Ogallala aquifer in the High Plains region is the largest aquifer, supplying irrigation water to 10.4 million acres or 1/5 of all the irrigated land in the country. Renewable groundwater is replenished via percolation of precipitation water. Changes in precipitation affect replenishment.
The simplest proof that groundwater withdrawals are beyond recharge capabilities is a falling water table. A water table is the upper water level of an underground area filled with water. Groundwater can create cavities in the ground. A sinkhole happens when an underground cavern is drained of its groundwater and suddenly collapses.