scope:

This part of ISO 9308 specifies a method for the enumeration of E. coli and coliform bacteria. The method is based on membrane filtration, subsequent culture on a chromogenic agar medium and calculation of the number of target organisms in the sample. Due to the low selectivity of the differential agar medium, background growth can interfere with the reliable enumeration of coliform bacteria and E. coli, for example in surface waters or shallow well waters. This method is not suitable for these types of water. This part of ISO 9308 is especially suitable for waters with low bacterial numbers that will cause less than 80 total colonies on chromogenic coliform agar. These may be drinking water, disinfected pool water or finished water from treatment plants.