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.