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 supplies 95% of the state's drinking water. 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.

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.

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.

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 Around nine billion gallons of ground water are withdrawn every day for various uses.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. See Estimated Use of Water in the United States in 2000 (USGS Publication) for more information on water use throughout the United States.

DEQ is responsible for protecting the quality of ground water in Idaho, but does not undertake this task alone. DEQ monitors and protects ground water in Idaho through partnerships 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. The Idaho Ground Water Quality Plan, the Ground Water Quality Rule (pdf on Department of Administration Web site), and the Idaho Ground Water Protection Interagency Cooperative Agreement (pdf 47 kb, 15 pages) outline the roles of DEQ, IDA, and IDWR.

It is DEQ's job to protect the quality of ground water in Idaho. A potential source of contamination of ground water is land application of wastewater (spent or used water from a home, community, farm, or industry). To assure ground water is protected, DEQ requires anyone wishing to land-apply wastewater to obtain a wastewater reuse permit. Septic systems can also contaminate ground water. Applicants for all large soil absorption septic systems and for central septic systems located in nitrate priority areas or in areas of "sensitive resource" aquifers must complete a nutrient-pathogen evaluation of the proposed wastewater system as part of their application for a permit. This evaluation helps predict whether effluent from the treatment system will be diluted enough to prevent ground water contamination. Read more about ground water protection activities.

DEQ conducts regional and local ground water quality monitoring. When routine monitoring results show exceedances of state or federal standards, DEQ follows up with ground water quality investigations in the area of the detection, then summarizes the results. Read more about ground water quality monitoring in Idaho.

These plans outline strategies for improving ground water quality in high priority areas. The strategies focus on prevention, protection, and remediation to maintain or improve water quality and prevent impairment of beneficial uses. The Idaho Ground Water Quality Plan is a master, interagency plan that explains these strategies in depth. Read more about Idaho's ground water quality management plans.

DEQ staff are members of Idaho's CAFO Site Advisory Team, along with staff from ISDA (team lead) and IDWR. The team reviews sites proposed for CAFOs, determines environmental risks, and submits site suitability determinations (View Idaho statute).

Ground water supplies 95% of Idaho's drinking water, so the quality of Idaho's ground water affects nearly everyone in the state. Two topics that relate directly to this issue, degraded ground water and ground water and private wells, are highlighted below. Click here for more information on drinking water issues (including arsenic in drinking water) and source water assessments and drinking water protection (source water is ground water that is used as a public drinking water source).

Idaho's ground water quality monitoring shows that ground water has been significantly degraded in specific areas across the state. This negatively impacts water quality and potentially threatens domestic water supplies, aquaculture, agriculture, mining, industrial, and other ground water beneficial uses.

Nitrate is one of the contaminants responsible for this degradation and is one of the most widespread ground water contaminants in Idaho. High levels of nitrate in drinking water are associated with adverse health effects in humans and livestock. High levels of nitrate also adversely affect fish and surface waters such as lakes and rivers.

The presence of nitrate (among other factors) has been used to develop a priority list of 25 degraded ground water quality areas throughout Idaho. While nitrate is just one of the potential ground water contaminants in Idaho, more is known about nitrate in ground water in Idaho than other contaminants. In addition, the presence of nitrate is a good indicator of other potential water quality problems. Read more about nitrate in ground water.

Private wells bring ground water to the surface for use in homes and businesses that aren't connected to public water supplies. About one-third of Idaho's citizens get their water from private wells. Since wells are drilled into ground water aquifers, the contaminants present in ground water, such as nitrate, can be present in well water. Well owners are responsible for maintaining their wells and ensuring their water is safe to drink. Learn more about maintaining your well and testing for contaminants.

Ground water is vulnerable to contamination. Once ground water becomes contaminated, it is very difficult to clean up and the contamination may persist for long periods of time.

You can help prevent ground water contamination by:

• Properly disposing of hazardous materials such as paint, bleach, and cleaning products
• Carefully using pesticides and fertilizers (DEQ Brochure, October 2007: pdf 143 kb, 2 pages)
• Watering your lawn wisely
• Maintaining your septic system

Read EPA's A Citizen's Guide to Ground Water Protection (U.S. EPA pdf document) to learn more about what you can do to protect ground water.

Overview of Idaho Ground Water Quality Protection Laws

(DEQ Brochure, June 2007: pdf 163 kb, 2 pages)