Testing the Microbiological Quality of Water

A variety of different microorganisms is found in untreated water. Most of these organisms do not pose a health hazard to humans. The organisms that operators are concerned with most are those that cause disease (pathogens), which include certain bacteria, viruses, and protozoa. These organisms influence the microbiological quality of water. Two common methods to determine microbiological water quality are the total coliform test and the standard plate count, both of which test for bacteria. This article explains why the coliform bacteria are used as indicator organisms and the procedures for the multiple‐tube fermentation and membrane filter technique tests. The standard plate count test method is covered also. A table accompanying the article lists various requirements of the National Primary Drinking Water Regulations for Microbiological Contamination. The following aspects are covered: maximum contaminant levels (MCLs) for the membrane filter and multiple‐tube fermentation tests; MCL violation; health effects; required sampling; check sampling; and the reporting requirement for check sampling.