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EPA-United States Environmental Protection Agency
Proposed Long Term 2 Enhanced Surface
Water Treatment Rule


TheEPA is proposing the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) to reduce disease incidence associated with Cryptosporidium and other pathogenic microorganisms in drinking water. The LT2ESWTR will supplement existing regulations by targeting additional Cryptosporidium treatment requirements to higher risk systems. This regulation also contains provisions to mitigate risks from uncovered finished water storage facilities and to ensure that systems maintain microbial protection as they take steps to reduce the formation of disinfection byproducts (DBPs).


Cryptosporidium is a protozoan parasite that is of particular concern in drinking water because it is resistant to disinfectants like chlorine and it has been associated with waterborne disease outbreaks. Ingestion of Cryptosporidium can cause acute gastrointestinal illness, and health effects in sensitive subpopulations (e.g., infants, AIDS patients, the elderly) may be severe, including the risk of death. Existing drinking water regulations require public water systems (systems) that use surface water sources and provide filtration to achieve at least a 99 percent (2-log) removal of Cryptosporidium. New data on Cryptosporidium infectivity, occurrence, and treatment indicate that current treatment requirements are adequate for the majority of systems, but there is a subset of systems with higher vulnerability to Cryptosporidium where additional treatment is necessary. This vulnerable subset includes those filtered systems with the highest source water Cryptosporidium levels, along with unfiltered systems (systems that use surface water sources and do not provide filtration).

About This Regulation

The LT2ESWTR will protect public health by supplementing existing drinking water regulations with additional risk-targeted treatment requirements for Cryptosporidium. This regulation will apply to all systems that use surface water or ground water under the direct influence of surface water. Cryptosporidium treatment: Under the LT2ESWTR, systems initially conduct source water monitoring for Cryptosporidium to determine their treatment requirements. Filtered systems will be classified in one of four risk bins based on their monitoring results. EPA projects that the majority of systems will be classified in the lowest risk bin, which carries no additional treatment requirements. Systems classified in higher risk bins must provide 90 to 99.7 percent (1.0 to 2.5-log) additional reduction of Cryptosporidium levels. The regulation specifies a range of treatment and management strategies, collectively termed the “microbial toolbox,” that systems may select to meet there additional treatment requirements. All unfiltered systems must provide at least 99 or 99.9 percent (2or 3-log) inactivation of Cryptosporidium, depending on the results of their monitoring. Monitoring: Cryptosporidium monitoring by large systems (serving at least 10,000 people) will begin six months after the LT2ESWTR is finalized and will last for duration of two years. Small systems (serving less than 10,000 people) are on a delayed schedule and will start monitoring when the required large system monitoring is finished. To reduce monitoring costs, small filtered systems will initially conduct one year of monitoring for E. coli, which is a bacterium that is less expensive to analyze than Cryptosporidium. These systems will be required to monitor for Cryptosporidium for one year only if their E. coli results exceed specified triggering concentrations. Systems must conduct a second round of monitoring beginning six years after the initial bin classification. Systems may grandfather equivalent previously collected data in lieu of conducting new monitoring, and systems are not required to monitor if they provide the maximum level of treatment required under the rule.