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Water: Stage 2 DBP Rule

Basic Information

EPA has developed the Stage 2 Disinfectants and Disinfection Byproducts Rule (DBP rule) to improve your drinking water quality and provide additional protection from disinfection byproducts. Your drinking water comes from source water locations such as:

  • Lakes
  • Rivers
  • Reservoirs
  • Ground water aquifers

Pathogens, such as Giardia, are often found in source water, and can cause gastrointestinal illness (e.g., diarrhea, vomiting, cramps) and other health risks. In many cases, water needs to be disinfected to inactivate (or kill) these microbial pathogens. However, disinfectants like chlorine can react with naturally-occurring materials in the water to form byproducts such as:

  • Trihalomethanes (THM)
  • Haloacetic acids (HAA)
  • Chlorite
  • Bromate

These byproducts, if consumed in excess of EPA's standard over many years, may lead to increased health risks. EPA has developed the Stage 2 DBP rule to protect public health by limiting exposure to these disinfectant byproducts.

Questions and Answers

See also: Information about Chloramine in Drinking Water


What is the Stage 2 DBP?
The Stage 2 DBP rule is intended to reduce potential cancer and reproductive and developmental health risks from disinfection byproducts (DBPs) in drinking water, which form when disinfectants are used to control microbial pathogens. Over 260 million individuals are exposed to DBPs.

This final rule strengthens public health protection for customers of systems that deliver disinfected water by requiring such systems to meet maximum contaminant levels as an average at each compliance monitoring location (instead of as a system-wide average as in previous rules) for two groups of DBPs, trihalomethanes (TTHM) and five haloacetic acids (HAA5). The rule targets systems with the greatest risk and builds incrementally on existing rules. This regulation will reduce DBP exposure and related potential health risks and provide more equitable public health protection. The Stage 2 DBPR is being released simultaneously with the Long Term 2 Enhanced Surface Water Treatment Rule to address concerns about risk tradeoffs between pathogens and DBPs.

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Who does this rule apply to?
The Stage 2 DBP rule applies to community and nontransient noncommunity water systems that add and/or deliver water that is treated with a primary or residual disinfectant other than ultraviolet light.

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What are the requirements of the final rule?
Under the Stage 2 DBP rule, systems will conduct an evaluation of their distribution systems, known as an Initial Distribution System Evaluation (IDSE), to identify the locations with high disinfection byproduct concentrations. These locations will then be used by the systems as the sampling sites for Stage 2 DBP rule compliance monitoring.

Compliance with the maximum contaminant levels for two groups of disinfection byproducts (TTHM and HAA5) will be calculated for each monitoring location in the distribution system. This approach, referred to as the locational running annual average (LRAA), differs from current requirements, which determine compliance by calculating the running annual average of samples from all monitoring locations across the system.

The Stage 2 DBP rule also requires each system to determine if they have exceeded an operational evaluation level, which is identified using their compliance monitoring results. The operational evaluation level provides an early warning of possible future MCL violations, which allows the system to take proactive steps to remain in compliance. A system that exceeds an operational evaluation level is required to review their operational practices and submit a report to their state that identifies actions that may be taken to mitigate future high DBP levels, particularly those that may jeopardize their compliance with the DBP MCLs.

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How long will it take for changes required by the Stage 2 DBP rule to be made?
The Stage 2 DBP rule builds incrementally on existing DBP rules. Many systems have already made significant progress in lowering their DBP levels. The Stage 2 DBP rule takes a risk-based targeted approach to require treatment changes by only those public water systems that are identified as having the greatest remaining risk. The first step is a multi-year process for systems to determine where higher levels of DBPs are likely to occur in their distribution system. These locations will become the system’s new DBP monitoring sites.

If the DBP levels at these locations are too high (i.e., above the MCL), the system will start to take corrective actions. These actions could range from simple, quickly implemented management or operational changes to major construction. Any changes made by systems must be well studied and planned before execution. This planning, obtaining funding and permits for construction, designing, and finally, constructing new facilities take time. The time to completion will vary depending on what they need to do. Depending on system size and the extent of needed construction, systems will begin the first year of compliance monitoring between 2012 and 2016 and must be in compliance with the Stage 2 DBP rule MCLs at the end of a full year of monitoring.

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What are the costs of the Stage 2 DBP rule?
The Stage 2 DBP rule will result in increased costs to public water systems and states. The rule applies to approximately 75,000 systems; a small subset of these will be required to make treatment changes. The average cost of the rule is $79 million annually (using a three percent discount rate).

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What are the benefits of the Stage 2 DBP Rule?
EPA has projected that the rule will prevent approximately 280 bladder cancer cases per year. Of these cases, 26% are estimated to be fatal. Based on bladder cancer alone, the rule is estimated to provide annualized mean monetized benefit of $1.5 billion. Additional non-quantified benefits such as those from preventing potential reproductive and developmental risks may also result.

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Is there funding associated with this rule?
Funding may be available from programs administered by EPA and other Federal agencies to assist systems in complying with the Stage 2 DBP rule. The Drinking Water State Revolving Fund (DWSRF) assists systems with financing the costs of infrastructure needed to achieve or maintain compliance with SDWA requirements. Through the DWSRF, EPA awards capitalization grants to States, which in turn can provide low-cost loans and other types of assistance to eligible systems.

In addition to the DWSRF, money is available from the Department of Agriculture’s Rural Utility Service (RUS) and Housing and Urban Development’s Community Development Block Grant (CDBG) program. RUS provides loans, guaranteed loans, and grants to improve, repair, or construct water supply and distribution systems in rural areas and towns of up to 10,000 people. The CDBG program includes direct grants to States, which in turn are awarded to smaller communities, rural areas, and coloñas in Arizona, California, New Mexico, and Texas and direct grants to U.S. territories and trusts.

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How was the Stage 2 DBPR developed?
These rules were developed from Federal Advisory Committee consensus recommendations. The Committee consisted of 21 organizational members representing EPA, State and local public health and regulatory agencies, local elected officials, Native American Tribes, large and small drinking water suppliers, chemical and equipment manufacturers, environmental groups, and other stakeholders.

The Stage 2 Microbial and Disinfection Byproducts Rules (M-DBP) are a set of interrelated regulations (the Stage 2 Disinfection Byproducts Rule and the Long Term 2 Enhanced Surface Water Treatment Rule) that address risks from microbial pathogens and disinfection byproducts. The Stage 2 M-DBP Rules are the final phase in the M-DBP rulemaking strategy, affirmed by Congress as part of the 1996 Amendments to the Safe Drinking Water Act (SDWA). Both the Stage 1 and Stage 2 M-DBP rules were developed using a consensus process.

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What are disinfection byproducts?
Disinfectants are an essential element of drinking water treatment because of the barrier they provide against waterborne disease-causing microorganisms. However, disinfection byproducts (DBPs) form when disinfectants used to treat drinking water react with naturally occurring materials in the water (e.g., decomposing plant material).

Total trihalomethanes (TTHM – chloroform, bromoform, bromodichloromethane, and dibromochloromethane) and haloacetic acids (HAA5 – monochloro-, dichloro-, trichloro-, monobromo-, dibromo-) are widely occurring classes of DBPs formed during disinfection with chlorine and chloramine. These DBPs generally form at much lower levels when chloramine is used instead of chlorine. The amount of trihalomethanes and haloacetic acids in drinking water from one water system can change from day to day, depending on the season, water temperature, amount of chlorine added, the amount of plant material in the water, and a variety of other factors.

At this time, EPA believes that the best way to control DBPs is both to regulate known byproducts and to limit the quantity of disinfection byproduct precursors (e.g., decomposing plant material) allowed to react with disinfectants. TTHM and HAA5 are useful indicators for measuring DBPs in chlorinated drinking water because they commonly occur at levels that can be easily measured.

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How does EPA regulate DBPs?
EPA has worked collaboratively with stakeholders over the last 15 years in developing regulations for DBPs. EPA believes that these regulations will decrease risks from DBPs in drinking water nationwide. EPA's current standards for DBPs provide the safest balance between the need to disinfect drinking water for protection against pathogens while safeguarding citizens from potentially harmful contaminants.

The Agency first regulated total trihalomethanes (TTHM) in 1979 at 100 parts per billion (ppb) [100 micrograms/liter (μg/L)] for systems serving at least 10,000 people. The Agency revised this rule when it issued the Stage 1 Disinfectants and Disinfection Byproducts Rule (Stage 1 DBPR) in December of 1998. The Stage 1 DBPR was the first phase in a rulemaking strategy required by Congress as part of the 1996 Amendments to the Safe Drinking Water Act. The Stage 1 DBPR set the maximum contaminant level for TTHM at 80 ppb and for the first time set a maximum contaminant level for five haloacetic acids (HAA5) at 60 ppb. These standards had to be met by the end of 2002 for surface water systems serving 10,000 or more people and by the end of 2004 for all other systems.

The Stage 2 DBPR was proposed in August 2003 and finalized on December 15, 2005. This rule builds on the other DBP rules. EPA believes that this regulation will further reduce exposure to DBPs and decrease potential cancer, reproductive, and developmental risks.

For more information:

The Stage 2 DBPR was proposed in August 2003 and promulgated on December 15, 2005. This rule builds on the other DBP rules. EPA believes that this regulation will further reduce exposure to DBPs and decrease potential cancer, reproductive, and developmental risks.

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How did the Agency weigh risks vs. benefits for disinfectant byproducts?
Disinfection byproducts are a special case because decreasing disinfection byproduct risk could increase risks from disease-causing microorganisms. Eliminating or significantly decreasing disinfection to stop disinfection byproduct formation would seriously compromise overall public health protection. The Agency’s priority is maintaining protection from disease-causing microorganisms. However, there are a number of things that water systems can do to reduce the levels of disinfection byproducts in drinking water (such as decreasing the amount of disinfectant and removing as much organic material as possible prior to disinfection).

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Why is drinking water disinfected?
Disinfecting tap water is critical to protect the public from disease-causing microorganisms. Chlorine is the most commonly used disinfectant. Drinking water is disinfected to kill bacteria, viruses, and other organisms that cause serious illnesses and deaths. Disinfection of drinking water has benefited public health enormously by lowering the rates of infectious diseases (for example, typhoid, hepatitis and cholera) spread through untreated water. In the beginning of the last century, prior to the disinfection of drinking water, tens of thousands of people died from disease-causing microorganisms in the water supply.

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What health risks are posed by disinfection byproducts such as THMs and HAAs?
To protect public health, EPA continues to strongly support both the disinfection of drinking water to reduce the risk of waterborne disease and the reduction of disinfection byproducts.

EPA has regulated DBPs since 1979 to address health risks posed by a potential association between chlorinated drinking water and cancer, particularly bladder cancer. Current reproductive and developmental health effects data do not support a conclusion at this time as to whether exposure to chlorinated drinking water or disinfection byproducts causes adverse developmental or reproductive health effects, but do support a potential health concern. Although uncertain, the combined health data warrant EPA’s promulgation of the Stage 2 Disinfection Byproduct Rule to provide an incremental step towards mitigating potential risks.

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