Bacteria and other microbes in public water supplies may pose immediate and serious health risks to humans. Since these contaminants are often difficult to detect through traditional testing, the Surface Water Treatment Rule (SWTR) requires most water sources to be treated through a system of disinfection and/or filtration. Disinfection is a process that exterminates disease?causing organisms in drinking water through the use of chemical oxidants such as chlorine, chlorine dioxide, and ozone. Disinfection is required for all surface water systems.

Filtration is a process by which particulate matter is removed from drinking water by passing the water through a filter. Filtration is required for all surface water systems and for groundwater systems under the direct influence of surface water that fail certain SWTR standards including those for coliforms, turbidity, Giardia lamblia, and residual disinfectants, among others.

Groundwater under the direct influence of surface water is any water beneath the surface of the ground with (1) significant occurrence of insects or other macroorganisms, algae, or large-diameter pathogens such as Giardia lamblia, or (2) significant and relatively rapid shifts in water characteristics such as turbidity, temperature, conductivity, or pH which closely correlate to weather or surface water conditions. Each state is responsible for defining whether ground water is under the direct influence of surface water.

Does The Surface Water Treatment Rule Apply to Your Community?

Yes, it applies to all public water supply systems (community and non-community) using a surface water source (i.e., water open to the atmosphere and subject to surface runoff) or a groundwater source under the direct influence of surface water.

Actions Your Community Should Be Taking

The SWTR requirements that apply to your water system will depend on the type of water source you use. For example, if your community uses a surface water system, you must be sure to disinfect and filter the water. In addition, you must send reports to the state documenting compliance with all treatment and monitoring requirements. If your system uses a groundwater source that is under the direct influence of surface waters (as determined by your state) and it exceeds applicable limits for coliform bacteria, turbidity, residual disinfectants, or other criteria (collectively called "filtration avoidance criteria"), then you must install filtration. Generally, filtration is not required for systems using groundwater under the direct influence of surface water that are able to meet all of the filtration avoidance criteria. Some states, however, automatically require the use of filters for all public water systems that use a ground water source under the influence of surface water. Check with your state concerning its policy regarding the use of filtration.

All public water supplies must be operated by personnel that meet qualifications specified by the state or EPA. The water supplier is required to monitor the water system, by sampling and testing the water, for compliance with the applicable maximum contaminant levels (MCLs). This requirement pertains to both surface water systems and groundwater systems under the direct influence of surface water Reports documenting this compliance must be sent to the state.

Timetable

Compliance timetables under the Surface Water Treatment Rule are as follows:

Surface water systems currently using filtration and disinfection

• A revised turbidity standard (0.5 nephelometric turbidity units [NTU]) and new disinfection requirements took effect July 1, 1993.
• New filtration avoidance criteria, disinfection criteria and monitoring and reporting requirements were required to be met beginning July 1, 1993.

Surface water systems currently using disinfection only

• Public water systems were required to begin new monitoring and reporting requirements for unfiltered systems starting December 30, 1991, and to meet the new monitoring and reporting requirements by January 1, 1992.
• States had to determine before December 30, 1991, which systems are required to filter.
• If filtration is required, it was required to be installed before June 29, 1993, or 18 months after your drinking water supply system fails to meet the filtration avoidance criteria.
• If the state determined before December 30, 1991, that an unfiltered drinking water system must filter, the system was required to comply with the existing interim turbidity standard until June 29, 1993, or until filtration is installed, whichever is later.

Surface water systems currently using no treatment

• Surface water systems must disinfect.
• If required by the state, surface water sources were required to install filtration by June 29, 1993, or 18 months after the drinking water system fails to meet the avoidance criteria.

Systems using a groundwater source

• For each system using a groundwater source, the state must determine whether that source is under the direct influence of surface water.
• If the state determines that a public water system is under the influence of surface water:
  • The system must begin sampling for the avoidance criteria within 6 months.
  • The system must begin meeting the avoidance criteria 18 months after the determination.
  • Failure to meet the avoidance criteria after 18 months may result in that public water system having to install filtration.

Additional Information

The surface water (and groundwater under the direct influence of surface water) treatment requirements are published in Title 40 Code of Federal Regulations Part 141.70 - 141.75.

EPA's "Guidance Manual for Compliance with the Filtration and Disinfection Requirements for Public Water Systems Using Surface Water," PB-89-207-047, available from the National Technical Information Service at 1/800/553-6847.

Contact your state drinking water agency for additional information regarding certain reporting requirements.

For further information on the federal requirements, contact the EPA Safe Drinking Water Hotline Telephone: 1/800/426-4791.

(See Resource Section for drinking water contacts)