Frequent Questions

05. What are EPA?s drinking water regulations for pathogens and indicators?

In 1974, Congress passed the Safe Drinking Water Act. This law requires EPA to determine the level of contaminants 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 contaminant level goals (MCLG). Contaminants are any physical, chemical, biological or radiological substances or matter in water. EPA sets MCLGs based on the best available science to prevent potential health problems.

For most contaminants, EPA sets an enforceable regulation called a maximum contaminant level (MCL) based on the MCLG. MCLs are set as close to the MCLGs as possible, considering cost, benefits and the ability of public water systems to detect and remove contaminants using suitable treatment technologies. When there is no reliable method that is economically and technically feasible to measure a contaminant at particularly low concentrations, a treatment technique is set rather than an MCL. A treatment technique is an enforceable procedure or level of technological performance which public water systems must follow to ensure control of a contaminant. States may set a more stringent MCL or treatment technique level for pathogens and indicators in drinking water than EPA.

Treatment Techniques Pertaining to Pathogens

Pathogen

MCLG

Treatment Technique and Regulation(s)

Cryptosporidium

Zero

Surface Water Treatment Rule requirements:
Systems using surface water or ground water under the direct influence of surface water (GWUDI) must disinfect and filter their water so that 99 percent of Cryptosporidium oocysts are removed or inactivated (killed). Unfiltered systems (systems that meet criteria for avoiding filtration) are required to include Cryptosporidium in their existing watershed control provisions.

Giardia lamblia

Zero

Surface Water Treatment Rule requirements:
Systems using surface water or GWUDI must disinfect and filter their water so that 99.9 percent of Giardia lamblia is removed or inactivated. Unfiltered systems (systems that meet criteria for avoiding filtration) are also required to include Giardia lamblia in their existing watershed control provisions.

Viruses

Zero

Surface Water Treatment Rule requirements:
Systems using surface water or GWUDI must disinfect and filter their water so that 99.99 percent of viruses are removed or inactivated.

For Ground Water Rule requirements pertaining to viruses, see “Fecal Indicators” in the Indicators table below.

Legionella

Zero

Surface Water Treatment Rule requirements:
Systems using surface water or GWUDI must (1) disinfect their water, and (2) filter their water or meet criteria for avoiding filtration.

There is no limit specific to Legionella, but EPA believes that if Giardia lamblia and viruses are removed/inactivated according to the treatment techniques in the surface water treatment rules, Legionella will be controlled.

 

Treatment Techniques and MCLs Pertaining to Indicators

Indicator

MCLG

Treatment Techniques and MCLs and Regulation(s)

Turbidity

No MCLG

Surface Water Treatment Rule requirements:

  • EPA’s surface water treatment rules require systems using surface water or GWUDI to (1) disinfect their water, and (2) filter their water or meet criteria for avoiding filtration so that:
  • Surface water systems and GWUDI systems that use conventional and direct filtration: At no time can turbidity (cloudiness of water) be higher than one nephelometric turbidity unit (NTU); samples for turbidity must be less than 0.3 NTU in at least 95 percent of samples in any month.
  • Surface water systems and GWUDI that use slow sand filtration or diatomaceous earth filtration: Follow state limits, which must be at least as stringent as the following: Turbidity must at no time exceed 5 NTU; samples for turbidity must be less than 1 NTU in at least 95 percent of samples in any month.
  • Surface water systems and GWUDI that use alternative filtration (technologies for filtering other than conventional, direct, slow sand, and diatomaceous earth filtration): Follow state limits, which should be at least as stringent as the following: Turbidity must not exceed 5 NTU;samples for turbidity must be less than 0.5 NTU in at least 95 percent of samples in any month.

    These standards, in combination with disinfection, must ensure that the system reliably achieves required pathogen control on a continuing basis.

 Total coliforms

Zero

Total Coliform Rule requirements:
Systems are required to take samples for total coliforms based on the population served, source type and vulnerability to contamination. No more than 5.0 percent of samples for total coliforms can be positive in one month. (For systems that collect fewer than 40 routine samples per month, no more than one sample can be total coliform-positive per month). If a sample tests positive for total coliforms, the system must collect a set of repeat samples within 24 hours, and also analyze for fecal coliform or E. coli.

Fecal coliforms and E. coli

Zero

Total Coliform Rule requirements:

  • A routine sample that tests positive for fecal coliform or E. coli triggers repeat samples. If  any repeat sample tests positive for total coliform, the system has an acute MCL violation.
  • A routine sample that tests positive for total coliform but tests negative for fecal coliform or E. coli triggers repeat samples. If any repeat sample then tests positive for fecal coliform or E. coli, the system has an acute MCL violation.

For Ground Water Rule requirements pertaining to E. coli, see Enterococci, and coliphage in the Indicators table below.

Fecal indicators (Enterococci or coliphage), and E. coli

Coliphage and Enterococci: No MCLG
E. coli: Zero

Ground Water Rule:
Public water systems that use ground water* must take corrective action if a sufficient deficiency is identified, or if the initial source sample (if required by the state) or one of the five additional ground water source samples tests positive for fecal contamination  (E. coli, Enterococci, or coliphage). The systems must implement at least one of the following corrective actions:

  • Correct all significant deficiencies
  • Provide an alternate source of water
  • Eliminate the source of contamination
  • Provide treatment that reliably achieves at least 4-log treatment of viruses (using inactivation, removal, or a state-approved combination of 4-log virus inactivation and removal) before or at the first customer for the ground water source.

* Including consecutive systems, but not PWS that combine all of their ground water with surface water or with ground water under the direct influence of surface water prior to treatment.

The following drinking water regulations apply to pathogens and indicators:
•  Total Coliform Rule
The Total Coliform Rule set both health goals and legal limits for total coliform levels in drinking water. The rule also details the type and frequency of testing that water systems must do.
•  Surface Water Treatment Rule (SWTR)
The Surface Water Treatment Rule seeks to prevent waterborne diseases caused by viruses, Legionella, and Giardia lamblia. These disease-causing microbes are present at varying concentrations in most surface waters. The rule requires that water systems filter and disinfect water from surface water sources to reduce the occurrence of unsafe levels of these microbes.
•  Interim Enhanced Surface Water Treatment Rule (IESWTR)
The Interim Enhanced Surface Water Treatment Rule improves control of microbial contaminants, particularly Cryptosporidium, in systems using surface water, or ground water under the direct influence of surface water, that serve 10,000 or more persons. The rule builds upon the treatment technique requirements of the Surface Water Treatment Rule.
•  Filter Backwash Recycling Rule (FBRR)
The Filter Backwash Recycling Rule requires public water systems (PWSs) to review their backwash water recycling practices to ensure that they do not compromise microbial control.
•  Long Term 1 Enhanced Surface Water Treatment Rule (LT1ESWTR)
The Long Term 1 Enhanced Surface Water Treatment Rule strengthens control of microbial contaminants, particularly Cryptosporidium, for small systems—those systems serving fewer than 10,000 people. It is the smaller system counterpart of the Interim Enhanced Surface Water Treatment Rule.
•  Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR)
LT2 rule is to reduce illness linked with the contaminant Cryptosporidium and other disease-causing microorganisms in drinking water.
•  Ground Water Rule (GWR)
Ground Water Rule specifies the appropriate use of disinfection while addressing other components of ground water systems to ensure public health protection.
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 reviewed the Total Coliform Rule as part of the Six Year Review and plans to propose revisions in 2010. EPA will include the surface water treatment rules in future Six Year Review cycles.
•  Total Coliform Rule Revisions
•  More information on the Six Year Review of Drinking Water Standards

 

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