Protecting Public Health and the Environment.

Ground Water in Idaho

Ground water is a key resource supporting many aspects of Idaho's way of life. It replenishes our streams and rivers and provides fresh water for irrigation, industry, and communities. In addition, ground water is the source of drinking water for 95% of Idaho citizens. As Idaho's population grows, so does the need for clean, usable ground water.

DEQ is responsible for protecting the quality of ground water in Idaho and relies on a combination of programs to protect ground water from pollution, clean up degraded ground water, and monitor and assess ground water quality. DEQ's ground water policy is to maintain and protect the existing high quality of Idaho's ground water and restore degraded ground water where feasible to support ground water beneficial uses. DEQ partners with the Idaho State Department of Agriculture (ISDA), Idaho Department of Water Resources (IDWR), and many other state, local, and private agencies, organizations, businesses, and individuals to achieve this goal.

The Water Cycle and Ground Water Movement

Ground water is simply water beneath the earth's surface. It is the water that fills the natural open spaces in soil and rocks underground in much the same way as water fills a sponge. It can be found at various depths at any location beneath the earth's surface. Springs are ground water that flows out of the earth.

Ground water is part of the water, or hydrologic, cycle, which is the cyclic movement of water from the air to the earth, into the earth, back to the surface, and eventually back to the air. Not all water completes all of these steps.

Hydrologic Cycle

When water falls to the earth as precipitation, some of it runs off the earth's surface into streams, rivers, lakes, and oceans. The sun's heat causes some water to evaporate; other water forms a vapor as it leaves plants (transpiration). Evaporation and transpiration provide the moisture that ultimately forms clouds and creates precipitation.

Water also infiltrates the ground where it renews the water supply. First it moves through the soil and an unsaturated zone where air fills most of the pores (spaces) in the soil and rock. Eventually, the water may reach an area where the pores between the rock and sediment are filled with water (the saturated zone). This zone is referred to as an aquifer. In an unconfined aquifer, the top of this zone is called the water table; the water in an aquifer is ground water.

Eventually, the water may leave the aquifer. Ground water can flow naturally from springs or canyon walls, supply water to rivers, or be pulled into wells. Once on the surface, the water may evaporate or again infiltrate the earth's surface as the cycle continues.

How Ground Water is Used in Idaho

Ground water is a vital resource in Idaho. Around nine billion gallons of ground water are withdrawn every day for various uses.

The water that flows from your tap likely comes from ground water, as it provides 95% of the state's drinking water. However, drinking water accounts for only around 4% of total ground water withdrawals each year.

Agriculture uses approximately 60% of the total ground water withdrawn. The water is used for irrigation of such crops as potatoes, sugarbeets, and barley. Aquaculture also relies on ground water, as do industrial processes that use ground water for food processing, fertilizer production, and high-tech manufacturing. Estimated Use of Water in the United States in 2005, a United States Geological Survey publication, provides more information on water use throughout the United States.


An aquifer is a natural underground area where large quantities of ground water fill the spaces between rocks and sediment. About 70 major aquifers have been identified in Idaho. Aquifers are valuable and protected resources. Learn more.

Sole Source Aquifers

A sole source aquifer is an aquifer that has been designated by the United States Environmental Protection Agency as the sole or principal source of drinking water for an area. As such, a designated sole source aquifer receives special protection. Learn more.

Private Wells

Public water suppliers are required to test their drinking water regularly and make these tests results available to the public. If you use a private well, it is your responsibility to maintain the well and ensure your water is safe to drink. To do this, periodically test the well water for contaminants and protect the wellhead. Learn how to protect the wellhead and what to do if you have problems with water quality here.

Protecting Ground Water Quality

Any type of hazardous material that soaks into the ground has the potential to contaminate ground water resources. It is much easier and cost-effective to protect our ground water than it is to remediate after contamination has occurred. Learn what you can do to protect ground water here

Ground Water Monitoring

Ground water is vulnerable to contamination. Monitoring of ground water quality is undertaken statewide by the Idaho Department of Water Resources and the United States Geological Survey's Water Resources Division to assess the current condition of Idaho's ground water quality, identify potential problem areas, and detect trends in ground water quality. DEQ conducts regional and local ground water quality monitoring and approves and oversees monitoring programs conducted for aquifer recharge projects and mining activities. Learn more.



Degraded Ground Water

Ground water supplies 95% of Idaho's drinking water, so the quality of Idaho's ground water affects nearly everyone in the state. Although the quality of ground water in Idaho is generally good, ground water quality monitoring shows that in specific areas of the state, Idaho's ground water has been significantly degraded. Learn more.

Nitrate in Ground Water

Although the quality of ground water in Idaho is generally good, ground water quality monitoring shows that in specific areas of the state, Idaho's ground water has been significantly degraded. Nitrate is one of the contaminants responsible for this degradation and is one of the most widespread ground water contaminants in Idaho. The presence of nitrate is a good indicator of other potential water quality problems as well. Learn more.

Ground Water Reports by Geographic Area

Technical reports on ground water contaminants at various locations around the state and other site-specific ground water documents may be accessed here.

Ground Water Management Plans

If ground water is already contaminated, DEQ's role is to help restore ground water quality and prevent further degradation. In coordination with other agencies, including the Idaho State Department of Agriculture and Idaho Department of Water Resources, DEQ assists local ground water quality advisory groups to develop ground water quality management strategies (compiled into ground water quality management plans) for high priority areas. View plans completed to date.