Bacteria are one-celled microscopic organisms; they occur just about everywhere, including our surface water. Ideally, municipal water supplies are disinfected to kill harmful bacteria, then periodically checked. Because there are so many different strains of bacteria, it would be impossible to test for each one. Instead, water departments look for an 'indicator organism,' something that suggests contamination could be occurring. Coliform bacteria is the most common indicator used. These bacteria occur in the colon of warm-blooded animals, among other places. While not usually harmful themselves, coliform bacteria do indicate the possibility of other, more dangerous organisms in the water. However, the presence or absence of coliform bacteria is no absolute guarantee; it's simply a first step in finding disease-causing organisms. Agencies may also test for E. Coli bacteria, which is a stronger sign of contamination. Another test is the standard or heterotrophic (het er oh TROF ic) plate count, which measures a broad spectrum of bacteria. It doesn't tell you if harmful bacteria are present, but a high plate count does mean poor overall water quality. To find out more about bacteria in the water, contact your local water department, or a water conditioning company.