In 1974, Congress passed the Safe Drinking Water Act. This law requires EPA to determine the level of residual disinfectants in drinking water at which no adverse health effects are likely to occur. These non-enforceable health goals, based solely on possible health risks and exposure over a lifetime, with an adequate margin of safety, are called maximum residual disinfectant level goals (MRDLG). Contaminants are any physical, chemical, biological or radiological substances or matter in water. EPA sets MRDLGs based on the best available science to prevent potential health problems.
Based on the MRDLG, EPA has set enforceable regulations for disinfectants, called a maximum residual disinfectant level (MRDL), at the following levels:
|Chloramine||4 milligrams per liter (mg/L) or 4 parts per million (ppm)||4.0 mg/L or 4 ppm as an annual average|
|Chlorine||4 mg/L or 4 ppm||4.0 mg/L or 4 ppm as an annual average|
|Chlorine Dioxide||0.8 mg/L or 800 parts per billion (ppb)||0.8 mg/L or 800 ppb|
MRDLs are set as close to the health goals as possible, considering cost, benefits and the ability of public water systems to detect and remove contaminants using suitable treatment technologies. In this case, the MRDL equals the MRDLG, because analytical methods or treatment technology do not pose any limitation. States may set more stringent drinking water MRDLGs and MRDLs for disinfectants than EPA.
The following drinking water regulations apply to disinfectants and disinfection byproducts:
- Stage 1 Disinfectants and Disinfection Byproducts Rule (Stage 1 DBP) (December 16, 1998)
The Stage 1 Disinfectants and Disinfection Byproducts Rule reduces exposure to disinfection byproducts for customers of community water systems and non-transient non-community systems, including those serving fewer than 10,000 people, that add a disinfectant to the drinking water during any part of the treatment process.
- Stage 2 Disinfectants and Disinfection Byproducts Rule (Stage 2 DBP) (December 15, 2005)
Stage 2 DBP rule builds upon earlier rules that addressed disinfection byproducts to improve your drinking water quality and provide additional public health protection from disinfection byproducts.
The Safe Drinking Water Act requires EPA to periodically review the national primary drinking water regulation for each contaminant and revise the regulation, if appropriate, based on new scientific data. EPA will include the Disinfectants and Disinfection Byproducts rules in future review cycles.