This Standard describes a reference method (Standard Test) for the detection and enumeration of Escherichia coli and coliform bacteria in water for human consumptiom. The Standard Test is based on membrane filtration, subsequent culture on a different agar medium and calculation of the number of target organisms in the sample. The Standard Test has a low selectivity, allowing 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. The standard is therefore especially suitable for disinfected water and other drinking waters of low bacterial numbers. The standard includes a rapid method (Rapid Test) for the detection of E.coli only within 24 h, which can be useful in special cases, when quick information is needed. The Rapid Test is based on membrane filtration, subsequent culture under selective conditions and calculation of the number of E.coli in the sample.