Drinking Water Contaminants - Escherichia coli,
E. coli (Continued)
How will I know if my water is safe?
If you get your water from a public water system, then your water system is required by law to notify you if your water is not safe. If you are interested in obtaining information about your drinking water, consult the water quality report that you should receive annually from your local water system, or call your local water system directly.
How is water treated to protect me from E. coli?
The water can be treated using chlorine, ultra-violet light, or ozone, all of which act to kill or inactivate E. coli. Systems using surface water sources are required to disinfect to ensure that all bacterial contamination is inactivated, such as E. coli. Systems using ground water sources are not required to disinfect, although many of them do.
If I have a private well, how can I have it tested for E. coli?
If you have a private well, you should have your water tested periodically. Contact your State laboratory certification officer to find out which laboratories have been certified for conducting total coliform analyses. (You may contact the Safe Drinking Water Hotline at 1-800-426-4791 for the address and phone number of this individual.) Then contact a certified lab near you and get instructions on how to send them a water sample. Typically, the lab will first test for total coliforms, which is a group of related organisms that is common in both the environment and in the gut of animals. If the sample is positive for total coliforms, the lab will determine whether E. coli is also present. E. coli is a type of total coliform that is closely associated with recent fecal contamination. Few E. coli strains cause disease. However, the presence of any E. coli in a water sample suggests that disease-causing organisms, are also likely to be present.
One of the strains of E. coli that causes disease is E. coli O157:H7. EPA does not believe it necessary for an owner of a private well to test specifically for this organism under normal circumstances. If E. coli O157:H7 is present in your well, it is highly likely that other strains of E. coli are also present. If a well is E. coli-positive, regardless of strain, you should not drink the water unless it is disinfected. Several tests are available for determining whether E. coli O157:H7 is present, but they are somewhat more expensive than the standard E. coli tests and many labs may not have the expertise or supplies to perform these tests. Your state's laboratory certification officer should be able to tell you which laboratories can perform these tests, or you can contact the lab directly.
If my well is contaminated with E. coli, what can I do to protect myself?
If your well tests positive for E. coli, do not drink the water unless you boil it for at least one minute at a rolling boil, longer if you live at high altitudes. You may also disinfect the well according to procedures recommended by your local health department. Monitor your water periodically after disinfection to make certain that the problem does not recur. If the contamination is a recurring problem, you should investigate the feasibility of drilling a new well or install a point-of-entry disinfection unit, which can use chlorine, ultraviolet light, ozone, or reverse osmosis systems.
How does the U.S. Environmental Protection Agency regulate E. coli?
According to EPA regulations, a system that operates at least 60 days per year, and serves 25 people or more or has 15 or more service connections, is regulated as a public water system under the Safe Drinking Water Act. If a system is not a public water system as defined by EPA's regulations, it is not regulated under the Safe Drinking Water Act, although it may be regulated by state or local authorities.
Under the Safe Drinking Water Act, EPA requires public water systems to monitor for coliform bacteria. Systems analyze first for total coliform, because this test is faster to produce results. Any time that a sample is positive for total coliform, the same sample must be analyzed for either fecal coliform or E. coli. Both are indicators of contamination with animal waste or human sewage.
The largest public water systems (serving millions of people) must take at least 480 samples per month. Smaller systems must take at least five samples a month unless the state has conducted a sanitary survey (a survey in which a state inspector examines system components and ensures they will protect public health) at the system within the last five years.
Systems serving 25 to 1,000 people typically take one sample per month. Some states reduce this frequency to quarterly for ground water systems if a recent sanitary survey shows that the system is free of sanitary defects. Some types of systems can qualify for annual monitoring.
Systems using surface water, rather than ground water, are required to take extra steps to protect against bacterial contamination because surface water sources are more vulnerable to such contamination. At a minimum, all systems using surface waters must disinfect. Disinfection will kill E. coli O157:H7.
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