Testing of water potability by MPN
Water sample can be tested for its potability by using microorganisms as an indicator of fecal pollution. These indicators are usually common intestinal commensal bacteria which are universally present in and excreted in large numbers by man and animals. One such indicator organism is coliform. These coliforms are generally detected by presumptive coliform counts (PCC) using multiple tube tests.
In multiple tube test, measured volumes of water are added to a series of tubes containing a liquid indicator growth medium. The medium receiving one or more of the indicator bacteria show growth and characteristic color change. From the number and distribution of positive and negative reactions, the most probable number (MPN) of indicator organisms in the sample may be estimated by referring statistical tables.