Bacterial contamination cannot be detected by sight, smell or taste. The only way to know if a water supply contains bacteria is to have it tested.
The Environmental Protection Agency (EPA) requires that all public water suppliers regularly test for coliform bacteria and deliver water that meets the EPA standards. There is no requirement to have private water wells, springs or other sources tested, it is up to the individual homeowner. For public water supplies, the frequency of testing depends on the size of the population served. Bacteria test results are available from the supplier and there must be a public notification if the water supply does not meet the standard. Owners of private water supplies are responsible for having their water supply tested to ensure it is safe from bacterial contamination. Often, lending agencies require private water supplies be tested before home loans will be approved, including refinancing a loan.
Generally, private water supplies should be tested for bacterial safety as follows: