Disinfectants (such as chlorine) are the primary defense against diseases caused by microbiological contaminants in public water systems. More than 90 percent of surface water supply systems disinfect their water. Although disinfection is the single most important treatment technique used by public water supply systems, the disinfectants themselves can react with organic materials in source water to form disinfection by-products that may have adverse human health effects. Therefore, EPA has established maximum contaminant levels (MCLs) for several disinfection by-products commonly found in drinking water systems.

Do The Disinfectants And Disinfection By-Products Regulations Apply to Your Community?

Yes, all community and non-transient, non-community public water systems that serve 10,000 or more people and that add a disinfectant during any part of the treatment process are currently required to limit concentrations of certain disinfection by-products in their water system. Non-transient, non-community public water systems are those that are not community water systems and that regularly serve at least 25 of the same persons over 6 months per year, (e.g., schools, businesses with their own system). Variances may be available if the water comes from sources that are determined not to be at risk from microbiological contamination.

For public water systems serving less than 10,000 people, monitoring for disinfection by-products will be limited to systems vulnerable to by-product development, such as those with high levels of organic materials. Whether a particular system must monitor for disinfection by-products is determined by the state.

Actions Your Community Should Be Taking

Currently, if your community serves a population of 10,000 or more, then you must comply with the MCLs for a group of disinfection by-products called total trihalomethanes (TTHM). TTHM are the sum of the concentrations of trichloromethane (chloroform), dibromochloromethane, bromodichloromethane, and bromoform. The MCL for TTHM is 0.1 milligram per liter. MCLs and maximum residual disinfectant levels for other disinfectants and disinfection by-products have yet to be finalized. The proposed MCLs and maximum residual disinfectant levels are listed separately at the end of this section.

The requirements you must meet to ensure that your community's water source is protected from harmful levels of disinfectants and disinfection by-products depend on the type of water supply available to you and the way in which the system is managed.

If your water supply is surface water: you must contact your state agency to determine your schedule for compliance with the filtration and disinfection rules.

If your water supply is ground water and you are now adding a disinfectant: In preparation for the upcoming disinfectants/disinfection by-products standards, start regular disinfectant residual tests at some consumer taps to determine how much disinfection is available at the "end-of-the-line" in your system. This will help you plan for modifications in your disinfection process to meet the new standards when they are finalized.

If your water supply is ground water and you are NOT adding a disinfectant now:

• Check your coliform bacteria tests over the past three or four years. If your water supply has a history that includes
• some positive coliform tests, it is likely that you will be required to disinfect.
• If your water supply has no positive coliform tests, continue following proper sampling procedures in conjunction with good maintenance and operation procedures for your water supply and distribution systems.
• Consult the July 29, 1994 proposed rule to determine what EPA considers to be the best available technologies for limiting concentrations of residual disinfectants and disinfectant by-products. Look at and price different equipment for disinfection. Chlorination, either by gas, liquid solutions, or granular compounds, is the method used by most very small water supply systems. Costs vary and may not be out of reach for your community. Your state agency, engineer or an equipment supply firm can help you with this information.
• Visit neighboring communities that are disinfecting and see how they do it and what it costs.

Timetable

Surface water supplies are covered by final rules on filtration and disinfection that were published on June 29, 1989. These rules require the disinfection of all surface water supplies. Rules for general disinfection of all drinking water supplies were proposed on July 29, 1994 and include maximum contaminant levels and maximum residual disinfectant levels for a number of disinfectants and disinfection by-products. At present, four disinfection by-products (trihalomethanes) are regulated, but only in community water supplies serving populations of 10,000 or greater. The proposed rules would regulate disinfectants, expand the number of regulated disinfectant by-products, and reduce the MCL for ITHM (see the list below).

Additional Information

The Disinfectants and Disinfection By-Products requirements are published in Title 40 Code of Federal Regulations Parts 141.30, 141.72.

"Protecting our Drinking Water From Microbes," EPA, available by calling the EPA Safe Drinking Water Hotline Telephone: 1/800/426-4791.

Your state agency has materials available that describe the proper installation and use of disinfection equipment in small systems.

(See Resource Section for drinking water contacts)

Proposed Maximum Contaminant Levels (MCLs) for Organic and Inorganic By-Products

*Total trihalomethanes are the sum of the concentrations of bromodichloromethane, dibromochloromethane, bromoform, and chloroform. **Haloacetic acids (five) are the sum of the concentrations of mono-, di-, and trichloroacetic acids and mono? and dibromoacetic acids. *** EPA did not set an MCL for chloral hydrate because the TTHM and HM5 MCLs and the treatment technique for disinfection by-product precursor removal will control for chloral hydrate.