What is groundwater?
Groundwater is the water that soaks into the soil from rain or other precipitation and moves downward to fill cracks and other openings in beds of rocks and sand. It is, therefore, a renewable resource, although renewal rates vary greatly according to
environmental conditions.
It also is an abundant natural resource.
Of all the freshwater in the world (excluding polar ice caps), 95 percent is groundwater. Surface water (lakes and rivers) only make up three percent of our freshwater.
Groundwater’s importance to the environment
Hydrologists estimate, according to the National Geographic Society, U.S. groundwater reserves to be at least 33,000 trillion gallons — equal to the amount discharged into the Gulf of Mexico by the Mississippi River in the past 200 years.
At any given moment, groundwater is 20 to 30 times greater than the amount in all the lakes, streams, and rivers of the United States.
About a quarter of all U.S. rainfall becomes groundwater. Groundwater provides much of the flow of many streams; many lakes and streams are “windows” to the water table. In large part, the flow in a stream represents water that has flowed
from the ground into the stream channel. It’s estimated by the U.S. Geological Survey that about 30 percent of U.S. streamflow is from groundwater, although it is higher in some locations and less in others.
All the water of the Earth including the atmosphere, oceans, surface water, and groundwater participates in the natural system we call the hydrologic cycle. As water moves through all these elements repeatedly, the system is truly cyclical.
Groundwater's importance to people
While about 90 percent of our freshwater supplies lie underground, less than 27 percent of the water Americans use comes from underground sources, which illustrates the underutilization of groundwater. [1]
The United States uses 79.6 billion gallons per day of fresh groundwater for public supply, private supply, irrigation, livestock, manufacturing, mining, thermoelectric power, and other purposes. [2]
California pumps 10.7 billion gallons per day of groundwater for all purposes, a third more as much than the second-ranked state — Texas (8.02 bgd). [3]
More than 15.9 million water wells for all purposes serve the United States. [4]
Approximately 500,000 new residential wells are constructed annually, according to NGWA estimates. The construction of these vitally needed water supply systems involves the use of more than 18,460 drilling machines by an estimated 8,085 groundwater contracting
firms. [5]
NGWA has determined that 44 percent of the U.S. population depends on groundwater for its drinking water supply — be it from either a public source or private well. [6]
Private household wells constitute the largest share of all water wells in the United States — more than 13.249 million year-round occupied households have their own well. [7]
Other kinds of wells are used for municipal systems, industry, agriculture, and quality monitoring. Groundwater accounts for 33 percent of all the water used by U.S. municipalities. [8]
Michigan, with an estimated 1,121,075 households served by private water wells, is the largest state market, followed by Pennsylvania, North Carolina, New York, and Florida. [9]
Irrigation accounts for the largest use of groundwater in the United States. Some 57.2 billion gallons of groundwater are used daily for agricultural irrigation from 475,796 wells. [10] In 1900, the United States used only 2.2 billion gallons of groundwater
daily for irrigation from 17,000 wells.
More than 90 percent of the groundwater pumped from the Ogallala, the nation’s largest aquifer underlying some 250,000 square miles stretching from Texas to South Dakota, is used for agricultural irrigation. Representing about one-third of all U.S.
irrigated agriculture, it creates about $20 billion annually in food and fiber.
If spread across the surface of the entire United States, the Ogallala’s groundwater would cover all 50 states with 1.5 feet of water. Scientists estimate it could take 6,000 years to refill naturally if it were ever to be fully withdrawn.
[11]
Texas leads the nation in the number of irrigation wells with 81,511. [12]
The number of U.S. farms irrigated in 2018 was 231,474. [13]
The U.S. energy cost of pumping water for irrigation in 2018 was $2.4 billion, an average of $15,289 per farm. [13]
The top five states in irrigated acres in 2018 were California, Nebraska, Arkansas, Texas, and Idaho. These states accounted for 50 percent of U.S.-irrigated acres and 56 percent of water applied. [13]
The amount of water used for irrigation in 2018 was 83.4 million acre-feet, down 5.8 percent from 2013 (1 acre-foot = 325,851 gallons). [13]
[1] Estimated Use of Water in the United States in 2005, U.S. Geological Survey Circular 1344, October 2009
[2] Estimated Use of Water in the United States in 2005, U.S. Geological Survey Circular 1344, October 2009
[3] Ibid.
[4] Estimate prepared by the National Ground Water Association from various federal data sources at U.S. Environmental Protection Agency, U.S. Department of Agriculture, and the U.S. Census
[5] Estimate prepared by the National Ground Water Association from various Association-sponsored industry surveys
[6] Resident population of the United States in 2005 was 296,410,404, U.S. Census
[7] American Housing Survey, U.S. Bureau of the Census, 2008
[8] Estimated Use of Water in the United States in 2005, U.S. Geological Survey Circular 1344, October 2009; U.S. Environmental Protection Agency, Drinking Water and Ground Water Statistics 2007, March 2008
[9] U.S. Census, 1990 (best available data by state)
[10] U.S. Department of Agriculture, Farm and Ranch Irrigation Survey 2013, November 2014, and U.S. Geological Survey, June 2018 report on 2015 water use
[11] Scientific American Water 3.0, March 2008; Understanding Water Risks, World Wildlife Fund, March 2009; State of the Water Industry, TechKnowledgey Strategic Group, March 2009
[12] U.S. Department of Agriculture, Farm and Ranch Irrigation Survey 2013, November 2014
[13] Irrigation and Water Management Survey 2018, formerly the Farm and Ranch Irrigation Survey, December 2019