Source water is untreated water from streams, rivers, lakes, or aquifers (ground water) that is used to provide public drinking water and to supply private wells used for human consumption.

Source water assessments are reports written by DEQ that provide information on the potential contaminant threats to public drinking water sources. Communities can use source water assessments to implement drinking water source protection plans, programs, and activities.

Source water protection is a process that enables communities to protect ground water and surface water supplies that serve as a source for drinking water. Source water protection consists of voluntary or regulatory programs and activities that are typically implemented at the local level by a broad spectrum of community groups, including government, private entities, and individuals. A drinking water source protection plan is often developed by a community or a public water system to identify actions a community can implement to help prevent contamination of water that supplies its public water system.

Safe drinking water is fundamental for a healthy and economically vibrant community. Local governments play a primary role in the protection of a community's drinking water supply. The Idaho Environmental Protection and Health Act (I.C. § 39-126) mandates that state and local governments incorporate policies from the Idaho Ground Water Quality Plan into their programs and states that cities, counties, and other political subdivisions are also authorized and encouraged to implement ground water quality protection policies within their jurisdictions.

The Idaho Local Land Use Planning Act (I.C. § 67-6537) requires local governing boards to consider the impact on ground water quality when considering amending, repealing, or adopting a comprehensive plan. A comprehensive plan should consider protection of source water because a sustainable supply of clean and reliable drinking water is needed for the economic vitality of a community.

Preventing contaminants from entering the water that supplies a public water system minimizes potential problems, such as increased health risks, expanded drinking water monitoring requirements, additional water treatment requirements, or expensive environmental cleanup activities.

In many cases, public drinking water systems are not operated by local governments and do not have the authority needed to protect drinking water sources. Therefore, municipal and county governments have the responsibility and legal authority for enacting and enforcing drinking water source protection measures.