United States
Environmental Protection
Agency
Office of Water
(4607)
EPA816-F-01-012
June 2001
Drinking Water Priority Rulemaking:
Microbial and Disinfection Byproduct Rules
Disinfection of drinking water is one of the major public health advances in the 20th century. One hundred
years ago, typhoid and cholera epidemics were common throughout American cities and disinfection was a
major factor in reducing these epidemics. However, the disinfectants themselves can react with naturally-
occurring materials in the water to form unintended byproducts which may pose health risks.
Over the past ten years, we have also learned that there are specific microbial pathogens, such as
Cryptosporidium, that are highly resistant to traditional disinfection practices. In 1993, Cryptosporidium
caused 400,000 people in Milwaukee to experience intestinal illness. More than 4,000 were hospitalized, and
at least 50 deaths have been attributed to the disease. There have also been cryptosporidiosis outbreaks in
Nevada, Oregon, and Georgia over the past several years.
A major challenge for water suppliers is how to balance the risks from microbial pathogens and disinfection
byproducts. It is important to provide protection from these microbial pathogens while simultaneously
ensuring decreasing health risks to the population from disinfection byproducts (DBFs). The Safe Drinking
Water Act (SDWA) Amendments, signed by President Clinton in August 1996, required EPA to develop
rules to achieve these goals.
These new rules are a product of six years of collaboration between the water industry, environmental and
public health groups, and local, state and federal government. This fact sheet contains general information
about the two new rules and others that are a part of the Microbial-Disinfectants and Disinfection
Byproducts (M-DBP) Rules. Separate fact sheets focus on the Interim Enhanced Surface Water Treatment
Rule (EPA 816-F-01-013) and the Stage 1 Disinfectants and Disinfection Byproducts Rule (EPA 816-F-01-
014).
Schedule of M-DBP Rules
December 16, 1998 - Final Rule
JuneS, 2001 -Final Rule
Summer 2001 - Final Rule
Spring/Summer 2002 - Final Rule
May 2002 - Final Rule
Interim Enhanced Surface Water Treatment Rule and
Stage 1 Disinfectants and Disinfection Byproducts Rule
Filter Backwash Recycling Rule
Long Term 1 Enhanced Surface Water Treatment Rule
Ground Water Rule
Long Term 2 Enhanced Surface Water Treatment Rule and
Stage 2 Disinfectants and Disinfection Byproducts Rule
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Drinking Water Priority Rulemaking: Microbial and Disinfection Byproduct Rules
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PUBLIC HEALTH CONCERNS
Most Americans drink tap water that meets all existing health standards all the time. These new rules will
further strengthen existing drinking water standards and thus increase protection for many water systems.
In 1990, EPA's Science Advisory Board concluded that exposure to microbial contaminants such as
bacteria, viruses, and protozoa (e.g., Giardia lamblia and Cryptosporidium) was likely the greatest remaining
health risk management challenge for drinking water suppliers. Acute health effects from exposure to
microbial pathogens is documented and associated illness can range from mild to moderate cases lasting only
a few days to more severe infections that can last several weeks and may result in death for those with
weakened immune systems.
While disinfectants are effective in controlling many microorganisms, they react with natural organic and
inorganic matter in source water and the distribution system to form potentially harmful DBFs. Many of
these DBFs have been shown to cause cancer and reproductive and developmental effects in laboratory
animals. More than 200 million people consume water that has been disinfected. Because of the large
population exposed, health risks associated with DBFs, even if small, need to be taken seriously.
EXISTING REGULATIONS
Surface Water Treatment Rule - The Surface Water Treatment Rule, promulgated in 1989,
applies to all public water systems using surface water sources or ground water sources
under the direct influence of surface water. It establishes maximum contaminant level goals
(MCLGs) for viruses, bacteria and Giardia lamblia. It also includes treatment technique
requirements for filtered and unfiltered systems that are specifically designed to protect
against the adverse health effects of exposure to these microbial pathogens.
Total Coliform Rule - The Total Coliform Rule, revised in 1989, applies to all PWSs and
establishes a maximum contaminant level (MCL) for total coliforms.
Total Trihalomethane Rule - In 1979, EPA set an interim MCL for total trihalomethanes of
0.10 mg/1 as an annual average. This applies to any community water system serving at
least 10,000 people that adds a disinfectant to the drinking water during any part of the
treatment process.
Information Collection Rule - The Information Collection Rule, promulgated in 1996,
established monitoring and data reporting requirements for large public water systems
serving at least 100,000 people to support the M-DBP rulemaking process. This rule was
intended to provide EPA with information on the occurrence in drinking water of microbial
pathogens and DBPs. In addition, EPA collected engineering data on how PWSs currently
control such contaminants.
INTERIM ENHANCED SURFACE WATER TREATMENT
RULE AND STAGE 1 DISINFECTANTS AND DISINFECTION
BYPRODUCTS RULE
EPA published the Interim Enhanced Surface Water Treatment Rule and Stage 1 Disinfectants and
Disinfection Byproducts Rule in December 1998. The final rules resulted from formal regulatory
negotiations with a wide range of stakeholders that took place in 1992-93 and 1997.
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Interim Enhanced Surface Water Treatment Rule
The Interim Enhanced Surface Water Treatment Rule applies to systems using surface water, or ground
water under the direct influence of surface water, that serve 10,000 or more persons. The rule also includes
provisions for states to conduct sanitary surveys for surface water systems regardless of system size. The
rule builds upon the treatment technique requirements of the Surface Water Treatment Rule with the
following key additions and modifications:
• Maximum contaminant level goal (MCLG) of zero for Cryptosporidium.
2-log Cryptosporidium removal requirements for systems that filter.
• Strengthened combined filter effluent turbidity performance standards.
Individual filter turbidity monitoring provisions.
• Disinfection profiling and benchmarking provisions.
Systems using ground water under the direct influence of surface water now subject to the new rules
dealing with Cryptosporidium.
Inclusion of Cryptosporidium in the watershed control requirements for unfiltered public water systems.
• Requirements for covers on new finished water storage facilities.
Sanitary surveys, conducted by states, for all surface water systems regardless of size.
The Interim Enhanced Surface Water Treatment Rule, with tightened turbidity performance criteria and
required individual filter monitoring, is designed to optimize treatment reliability and to enhance physical
removal efficiencies to minimize the Cryptosporidium levels in finished water. In addition, the rule includes
disinfection benchmark provisions to assure continued levels of microbial protection while facilities take the
necessary steps to comply with new DBF standards.
Stage 1 Disinfectants and Disinfection Byproducts Rule
The final Stage 1 Disinfectants and Disinfection Byproducts Rule applies to community water systems and
non-transient non-community systems and transient non-community water systems using chlorine dioxide
MCLs, including those serving fewer than 10,000 people, that add a disinfectant to the drinking water during
any part of the treatment process.
The final Stage 1 Disinfectants and Disinfection Byproducts Rule includes the following key provisions:
• Maximum residual disinfectant level goals (MRDLGs) for chlorine (4 mg/L), chloramines (4 mg/L), and
chlorine dioxide (0.8 mg/L).
• Maximum contaminant level goals (MCLGs) for three trihalomethanes (bromodichloromethane (zero),
dibromochloromethane (0.06 mg/L), and bromoform (zero)), two haloacetic acids (dichloroacetic acid
(zero) and trichloroacetic acid (0.3 mg/L)), bromate (zero), and chlorite (0.8 mg/L).
• MRDLs for three disinfectants (chlorine (4.0 mg/L), chloramines (4.0 mg/L), and chlorine dioxide (0.8
mg/L)).
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• MCLs for total trihalomethanes (0.080 mg/L) - a sum of the three listed above plus chloroform,
haloacetic acids (HAAS) (0.060 mg/L)- a sum of the two listed above plus monochloroacetic acid and
mono- and dibromoacetic acids), and two inorganic disinfection byproducts (chlorite (1.0 mg/L)) and
bromate (0.010 mg/L)).
• A treatment technique for removal of DBF precursor material.
The terms MRDLG and MRDL, which are not included in the SDWA, were created during the negotiations
to distinguish disinfectants (because of their beneficial use) from contaminants. The final rule includes
monitoring, reporting, and public notification requirements for these compounds. This final rule also
describes the best available technology (BAT) upon which the MRDLs and MCLs are based.
FUTURE RULES
Long Term 1 Enhanced Surface Water Treatment Rule
While the Stage 1 Disinfectants and Disinfection Byproducts Rule will apply to systems of all sizes, the
Interim Enhanced Surface Water Treatment Rule only applies to systems serving 10,000 or more people.
The Long Term 1 Enhanced Surface Water Treatment Rule, expected in 2001, will strengthen microbial
controls for small systems (i.e. those systems serving fewer than 10,000 people). The rule will also prevent
significant increase in microbial risk where small systems take steps to implement the Stage 1 Disinfectants
and Disinfection Byproducts Rule.
EPA believes that the rule will generally track the approaches in the Interim Enhanced Surface Water
Treatment Rule for improved turbidity control, including individual filter monitoring and reporting. The rule
will also address disinfection profiling and benchmarking.
Long Term 2 Enhanced Surface Water Treatment Rule and Stage 2 Disinfectants and Disinfection
Byproduct Rule
The SDWA, as amended in 1996, requires EPA to finalize a Stage 2 Disinfectants and Disinfection
Byproducts Rule by May 2002. Although the 1996 Amendments do not require EPA to finalize a Long
Term 2 Enhanced Surface Water Treatment Rule along with the Stage 2 Disinfectants and Disinfection
Byproducts Rule, EPA believes it is important to finalize these rules together to ensure a proper balance
between microbial and DBP risks.
EPA began discussions with stakeholders in December 1998 on the direction for these rules. EPA
anticipates proposed rules in 2001. The intent of the rules is to provide additional public health protection, if
needed, from DBPs and microbial pathogens.
Ground Water Rule
EPA is finalizing the Ground Water Rule which specifies the appropriate use of disinfection and, just as
importantly, addresses other components of ground water systems to ensure public health protection. There
are more than 158,000 public ground water systems. Almost 89 million people are served by community
ground water systems, and 20 million people are served by non-community ground water systems.
Ninety-nine percent (157,000) of ground water systems serve fewer than 10,000 people. However, systems
serving more than 10,000 people serve 55 percent (more than 60 million) of all people who get their
drinking water from public ground water systems.
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Filter Backwash Recycling Rule
The Filter Backwash Recycling Rule establishes a standard to return all recycle flows to a point that
incorporates all treatment processes of the system's existing conventional or direct filtration systems or at an
alternate location approved by the state. The regulation will apply to public water systems that use surface
water or ground water under the direct influence of surface water, practice conventional or direct filtration,
and recycle spent filter backwash, sludge thickener supernatant, or liquids from dewatering processes. The
rule was promulgated on June 8, 2001.
ADDITIONAL INFORMATION
EPA encourages public input into regulation development. Public meetings and opportunities for public
comment on M-DBP rules are announced in the Federal Register. EPA's Office of Ground Water and
Drinking Water also provides this information for the M-DBP rules and other programs in its online
Calendar of Events.
For more information, contact EPA's Safe Drinking Water Hotline, 1-800- 426-4791, or see the Office of
Ground Water and Drinking Water web page at http://www.epa.gov/safewater/standards.html.
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