Bacteriological Quality.  The specific disease causing organisms present in water are not easily identified, and the techniques for comprehensive bacteriological examination are complex and time consuming. It has been necessary, therefore, to develop tests that indicate the relative degree of contamination in terms of a single, easily performed test.

Because many of the microorganisms that cause disease in man are transmitted through the fecal wastes of infected individuals, the most widely used method of testing the bacteriological quality of water involves testing for a single group of bacteria that are always present when fecal contamination is present. This group of bacteria, the coliform group, inhabits the intestinal tract of man, but is also found in most domestic animals, birds, and certain wild species. The methods used to test specifically for coliform are the membrane filter test and the multiple tube fermentation test. A third test, the heterotrophic (standard) plate count, determines the total number of bacteria in a sample that will grow under certain conditions.

Some groundwater sources, if properly protected and developed, can meet bacteriological drinking water standards without treatment. However, disinfection is a recommended safeguard for noncommunity systems and required treatment for community systems. Chlorination of ground water also introduces a disinfectant residual that helps maintain bacteriological quality of the water in the distribution system.

 Water from surface sources should always be disinfected, usually by chlorination, before it is supplied to the public. For both ground and surface water, protection of the source from contamination should be an ongoing priority.  In ground water sources, iron bacteria can cause problems with staining and tastes and odors. Proper well drilling procedures will prevent the entrance of iron bacteria into a new well, and iron bacteria in an existing well can usually be eliminated by temporarily introducing a high chlorine concentration.

 A well serving more than 25 people or having at least 15 connections is considered a public water supply and must comply with Pennsylvania Safe Drinking Water Regulations.