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Source Water

Source water is the untreated groundwater (e.g., aquifers and springs) and surface waters (e.g., rivers, streams, and lakes) used to supply drinking water to private, domestic wells and public water systems. Groundwater and surface water used for drinking water supplies are often vulnerable to contamination from land use practices such as farming and potential contaminant sources such as gas stations within the vicinity of drinking water wells and intakes. There are ways to minimize this vulnerability and help protect public drinking water from contaminants.

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A source water assessment provides information on the potential contaminant threats to public drinking water sources. As required by the Safe Drinking Water Act, Idaho completed and summarized assessments of all recognized public water sources. Each source water assessment report provides the following information

  • Defines the zone of contribution, which is that portion of the watershed or subsurface area contributing water to the well, spring, or surface water intake, known as source water area delineation.
  • Identifies the significant potential sources of drinking water contamination in those areas, known as potential contaminant source inventory.
  • Determines the likelihood that the water supply will become contaminated, known as a susceptibility analysis.

Source water assessments are the cornerstone of source water protection. Local communities can use the information gathered through the assessment process to create a broader source water protection program to address current problems and protect drinking water supplies.

Online Assessment Database—Source water assessment information for Idaho public water systems is accessible using the Source Water Assessment Database. The database provides information on assessed sources, including well, spring, or surface water intake, a potential contaminant inventory, contamination susceptibility ) summary, maps of the source water delineation, and a summary report. You can search the database by county, public water system number, water system name, and type of source.

Source Water Assessment Plan—In 1996, Congress amended the Safe Drinking Water Act to place more emphasis on the protection of surface water and ground water sources used for public drinking water. Each state with a public drinking water program was required to develop a source water assessment plan for public drinking water sources, conduct assessments on all public water systems, and make the assessments available to the public.

With input from a diverse group of stakeholders and Idaho’s Source Water Assessment Advisory Committee, DEQ completed the Idaho Source Water Assessment Plan and it was approved by EPA. To date, more than 3,500 public water system sources have been assessed and source water assessment reports completed.

Source water protection is a voluntary community effort to help prevent contamination of the source water that supplies its public water system. The effort may involve creating a source water or drinking water protection plan and implementing regulatory or non-regulatory management practices. Preventing contaminants from entering a public water system supply benefits the community by minimizing the problems that can occur from contaminants in the water supply such as increased health risks to the public, expanded drinking water monitoring requirements, additional water treatment requirements, and expensive environmental cleanup activities. Many Idaho communities have already developed a source water protection plan to help prevent contamination of their source water. The Source Water Protection Plan Map is an interactive map to learn about communities that have source water protection plans. Communities can learn more about source water protection and how to implement a source water protection program using the Community Guide for Source Water Protection Programs.

Source Water Protection Tool—The Source Water Protection Planning Tool assists public water systems in developing a source water protection plan and emergency response plan for their water system. The tool gathers information from existing databases, as well as input from user entry to create a planning document.

Activity Guide—The Source Water Protection Activity Guide is a tool for identifying potential sources and types of contamination that could threaten drinking water sources. It provides possible protection activities that public water systems, local governments, businesses, and individuals can implement to better protect source water from contamination.

Source water protection activities can include non-regulatory and regulatory approaches. Non-regulatory management practices and education and outreach can be effective by changing the behaviors and practices of those in the source water protection area. These strategies are most effective when combined with regulatory approaches such as land-use regulations, permitting, or other public policy strategies.

Use the Quick Select menus to navigate through the guide, learn about potential contaminant sources, and identify possible protection activities to minimize potential threats to source water. To learn more about a specific drinking water source and its susceptibility to contamination, read your system’s source water assessment report. 

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