Surface Water Treatment Rule

The Surface Water Treatment Rule (SWTR) seeks to prevent waterborne diseases caused by viruses, Legionella, and Giardia lamblia. These disease-causing microbes are present at varying concentrations in most surface waters. The rule requires that water systems filter and disinfect water from surface water sources to reduce the occurrence of unsafe levels of these microbes.

If a public water system uses a lake, river, stream or pond as its water source, then it is regulated by the Surface Water Treatment Rule.

The SWTR was published in the Federal Register by the Environmental Protection Agency (EPA) on June 29, 1989. Significant revisions were ordered in August, 1996, when the Safe Drinking Water Act was reauthorized by Congress. This rule contains provisions that require disinfection and filtration for all public water systems that use surface water or a source that is ground water under the direct influence of surface water.

Only those systems that were able to demonstrate compliance with the stringent source water quality criteria, meet the inactivation (contact time) requirements, and maintain an effective watershed control program obtained an avoidance to filtration. The State of Maine has thirteen (13) community water systems that qualify for filtration avoidance. The district compliance officer and field inspector annually inspect an unfiltered system's disinfection facilities, operations, and on-going source protection efforts.

The SWTR established Maximum Contaminant Levels (MCLs) for Turbidity, Heterotrophic Plate Count (Bacteria), Giardia Lamblia cysts, Legionella, and enteric viruses. The SWTR also published approved testing methodologies for the purpose of determining compliance. Approved testing procedures can be found in the Standard Methods text or 40 CFR Part 141. The monitoring requirements are dependent on the type of filtration and/or disinfections treatment employed by the system.

Documents, Forms, and Resources

• Alternative Filtration Technologies Guidebook (PDF)
• Contact Time Determination (PDF)
• Surface Water Treatment Rule Policies (PDF)
• Contact Time Tables for Giardia Lamblia Inactivation (PDF)
• Long Term 2 Rule Summary
• Sample Plan/Report Forms:
• Crypto Sample Plan/Report - Filtered Systems Greater Than 10000 Population
• Crypto Sample Plan/Report - Unfiltered Systems Greater Than 10000 Population
• Crypto Sample Plan/Report - Filtered Systems Less Than 10000 Population
• Crypto Sample Plan/Report - Unfiltered Systems Less Than 10000 Population
• E. coli Sample Plan/Report - Filtered Systems Less Than 10000 Population
• LT2 Microbial Toolbox Options
• Crypto Testing Waiver - Request for Exemption from Crypto Monitoring

For more information about the Surface Water Treatment Rule or Approved Alternative Filtration Technologies, please contact your Public Water System Inspector.

Updated 6/1/2023