scope:

This part of ISO 9308 describes a reference method (Standard Test) for the detection and enumeration of Escherichia coli and coliform bacteria in water for human consumption. The Standard Test is based on membrane filtration, subsequent culture on a differential agar medium and calculation of the number of target organisms in the sample.

The Standard Test has a low selectivity, allowing the detection of injured bacteria. Due to the low selectivity, background growth can interfere with the reliable enumeration of coliform bacteria and E. coli, for example in some drinking waters, like shallow well waters, that have not been disinfected and yield a high background growth.

This part of ISO 9308 is therefore especially suitable for disinfected water and other drinking waters of low bacterial numbers. This part of ISO 9308 includes a rapid method (Rapid Test) for the detection of E. coli only within 24 h in water for human consumption, which can be useful in special cases when information is needed quickly. The Rapid Test is based on membrane filtration, subsequent culture under selective conditions and calculation of the number of E. coli in the sample.

Standard and Rapid Tests described in this part of ISO 9308 are applicable to other kinds of water provided that suspended matter or background flora does not interfere with filtration, culture and counting.