Protecting Public Health and the Environment.

Source Water Assessments in Idaho

What Is a Source Water Assessment?

A source water assessment (SWA) summarizes the likelihood of individual drinking water sources becoming contaminated (usually a short-term "contamination event") and serves as a foundation for public water systems to prepare source water (drinking water) protection plans and implement protection measures. Each source water assessment report: 

  • 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 (source water area delineation)
  • Identifies the significant potential sources of drinking water contamination in those areas (potential contaminant source inventory)
  • Determines the likelihood that the water supply will become contaminated (susceptibility analysis)

Source water assessments are the cornerstone for 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 prevent future threats to the quality of their drinking water supplies. The information acquired from assessments also assists DEQ in overseeing public water systems.

History of SWAs in Idaho

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 in October 1999, and it was approved by EPA in November 1999. To date, more than 3,500 public water system sources have been assessed and source water assessment reports completed.

How to View a Source Water Assessment Report

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

The Source Water Assessment Database contains the most current source water assessment information for all assessments completed since 2000. The hard copy reports developed prior to 2009, when the SWA database was developed, may contain additional hydrogeologic information not captured in the current database. Scanned copies of the these reports as well as all available modeling reports can be found in the References section of the source water assessment summary reports found online.


Enter Source Water Assessment Database

DEQ State Office - Water Quality Division

1410 N. Hilton
Boise, ID 83706
(208) 373-0502

Staff Contacts

Source Water Coordinator
Rachael Smith
(208) 373-0249

DEQ Resources

DEQ Source Water Assessment Database User Guide

More Information

Source Water Assessment

Discover Drinking Water with DEQ
Presentation at the 2012 Idaho Environmental Education Association Conference describing the Source Water Assessment Online Tool and the Ground Water Quality Data Online Mapping Tool and how they can be used to teach students about Idaho’s drinking water sources. 

Related Pages

Source Water Protection in Idaho

Source Water Protection Grants

Source Water Protection Activity Guide

Ground Water in Idaho

Drinking Water in Idaho