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Water: Basic Information about Regulated Drinking Water Contaminants

Basic Information about Disinfectants in Drinking Water: Chloramine, Chlorine and Chlorine Dioxide

To protect drinking water from disease-causing organisms, or pathogens, water suppliers often add a disinfectant, such as chlorine, to drinking water. However, disinfection practices can be complicated because certain microbial pathogens, such as Cryptosporidium, are highly resistant to traditional disinfection practices. Also, disinfectants themselves can react with naturally-occurring materials in the water to form byproducts, such as trihalomethanes and haloacetic acids, which may pose health risks.

A major challenge for water suppliers is how to control and limit the risks from pathogens and disinfection byproducts. It is important to provide protection from pathogens while simultaneously minimizing health risks to the population from disinfection byproducts. For more information, see fact sheets on Pathogens and Indicators and Disinfection Byproducts.


What are disinfectants, how are they used, and what are their health effects in drinking water at levels above the maximum residual disinfectant level?
Disinfectant (Chemical Abstract Service Registry Number) Definition and uses Health Effects
Chloramine (as Cl2) (10599-90-3) Chloramine (as CI2) is a water additive used to control microbes, particularly as a residual disinfectant in distribution system pipes. It is formed when ammonia is added to water containing free chlorine. Monochloramine is one form of chloramines commonly used for disinfection by municipal water systems. Other chloramines (di- and tri-) are not intentionally used to disinfect drinking water and are generally not formed during the drinking water disinfection process. Some people who use water containing chloramine in excess of the maximum residual disinfectant level could experience irritating effects to their eyes and nose, stomach discomfort or anemia.
Chlorine (as Cl2)(10049-04-4) The gaseous or liquid form of chlorine (CL2) is a water additive used by municipal water systems to control microbes. It is relatively inexpensive and has the lowest production and operating costs and longest history for large continuous disinfection operations. Chlorine is a powerful oxidant. Some people who use water containing chlorine well in excess of the maximum residual disinfectant level could experience irritating effects to their eyes and nose. Some people who drink water containing chlorine well in excess of the maximum residual disinfectant level could experience stomach discomfort.
Chlorine dioxide (as ClO2)(10049-04-4) Chlorine dioxide is a water additive used to control microbes and can be used to control tastes and odors. It rapidly disappears from stored water. Some infants, young children, and fetuses of pregnant women who drink water containing chlorine dioxide in excess of the maximum residual disinfectant level could experience nervous system effects. Some people who drink water containingchlorine dioxide well in excess of the MRDL for many years may experience anemia.

This health effects language is not intended to catalog all possible health effects for disinfectants. Rather, it is intended to inform consumers of some of the possible health effects associated with disinfectants in drinking water when the rule was finalized.


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What are EPA’s drinking water regulations for disinfectants?
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:

Disinfectant MRDLG MRDL
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.


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How will I know if disinfectants are in my drinking water?
Public water systems using surface water or ground water under the direct influence of surface water are required to maintain a detectible disinfectant residual in the distribution system. When routine monitoring indicates that disinfectant levels are above the MRDL, your water supplier must take steps to reduce the amount of disinfectant so that it is below that level. For chlorine dioxide, water suppliers must notify their customers as soon as practical, but no later than 24 hours after the system learns of the violation. For chloramine and chlorine, water suppliers must notify their customers as soon as practical, but no later than 30 days after the system learns of the violation. Additional actions, such as providing alternative drinking water supplies, may be required to prevent serious risks to public health.


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How are disinfectants controlled in my drinking water?
The following treatment method(s) have proven to be effective for removing chloramines, chlorine, and chlorine dioxide to below their MRDLs: control of treatment processes to reduce disinfectant demand and control of disinfection treatment processes to reduce disinfectant levels.


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How do I learn more about my drinking water?
EPA strongly encourages people to learn more about their drinking water, and to support local efforts to protect the supply of safe drinking water and upgrade the community water system. Your water bill or telephone book’s government listings are a good starting point for local information.

Contact your water utility. EPA requires all community water systems to prepare and deliver an annual consumer confidence report (CCR) (sometimes called a water quality report) for their customers by July 1 of each year. If your water provider is not a community water system, or if you have a private water supply, request a copy from a nearby community water system.


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