Groundwater is a fundamental natural resource in the United States, representing a significant portion of the nation’s fresh water supply. This water exists underground in saturated zones, filling the pores and fractures within materials like sand, gravel, and rock. These water-bearing rock formations are known as aquifers, which act as naturally occurring reservoirs. The upper boundary of this saturated zone is called the water table.
Groundwater for Agricultural Irrigation
Groundwater withdrawal for agricultural irrigation represents the largest volume use of this resource across the country. Farmers rely heavily on aquifers to sustain crop production, particularly in arid regions where rainfall is insufficient. Approximately 54% of all irrigation water applied on US farms comes from groundwater sources, pumped from on-farm wells. This consistent water source allows for the cultivation of high-value crops that might otherwise fail due to drought.
Irrigation is especially concentrated in regions overlaying major aquifers, such as the High Plains Aquifer system, which includes the Ogallala Aquifer. This reservoir stretches across eight states and supports a large portion of all US irrigated land. Groundwater from the Ogallala is essential for growing major crops like corn, cotton, wheat, and soybeans. However, the water extraction rate often exceeds the natural rate of replenishment, creating a sustainability concern for future food production.
In the Texas High Plains, over 95% of irrigation water is extracted from groundwater, demonstrating the dependence of the local economy on this supply. Groundwater also provides supplemental water during dry spells in more humid environments, which helps stabilize crop yields. The reliance on this resource has increased significantly since the mid-20th century, driven by the adoption of large-scale irrigation technology like center-pivot systems.
Supplying Public Water Systems
Groundwater serves as a major source for public water systems, which treat and distribute drinking water to homes and businesses. Nearly 40% of the water used by these public supply systems is withdrawn from underground sources. These systems use large-capacity wells to pump water from aquifers to centralized treatment plants. The water is then processed to meet safety standards before being channeled through distribution networks.
The use of groundwater for public supply is governed by the Safe Drinking Water Act (SDWA). This act mandates that the Environmental Protection Agency (EPA) set national water quality standards. This regulatory oversight ensures that water delivered through public systems is monitored for contaminants, including microorganisms, chemicals, and radionuclides. Approximately 90 million American residents are served by community water systems that rely on groundwater.
The natural filtering capacity of the soil and rock layers often means groundwater requires less extensive treatment compared to surface water sources. This inherent quality makes it a reliable and cost-effective source for municipal use. However, the depth of the well and the geological composition of the aquifer determine the specific water quality and necessary purification processes.
Industrial and Power Generation Needs
The industrial sector and energy producers rely on groundwater for a variety of large-scale operations. Manufacturing processes, such as those in the chemical, paper, and metal industries, use groundwater for processing, washing, and cleaning products. The quality and consistent temperature of groundwater make it valuable for these industrial applications.
A significant portion of groundwater is directed toward the cooling systems of thermoelectric power plants, which generate electricity using coal, nuclear, or natural gas. These facilities withdraw substantial volumes of water to cool steam after it has turned the turbines. In arid regions like the Southwest, where surface water is scarce, power plants often rely on aquifers for this cooling process.
It is important to differentiate between water withdrawal and consumption in this sector. While thermoelectric power is a major water user by volume withdrawn, only a small fraction is “consumptive,” meaning it is lost to the atmosphere through evaporation. The majority of the withdrawn water is returned to the environment, though it is often warmer, which can impact local surface water ecosystems.
Private Well Use
Beyond centralized public water systems, groundwater is the sole source of water for millions of self-supplied domestic users, primarily in rural areas. Over 13 million households, representing more than 43 million Americans, rely on private wells for their drinking, cooking, and sanitation needs. These individual wells tap directly into local aquifers, providing a decentralized source of household water.
The regulatory environment for private wells differs significantly from that of public systems. The EPA does not regulate private wells under the Safe Drinking Water Act, meaning the well owner is solely responsible for ensuring the safety and quality of their water. This lack of federal oversight necessitates that owners perform their own regular testing for contaminants.