This document specifies the requirements for the performance testing of membrane filters used for the retention followed by direct enumeration of microorganisms by culture methods. This document is applicable to membrane filters which are used for retention followed by direct enumeration of specific microorganisms on solid media or on other devices containing media, like absorbent pads[19]. This document is not applicable for membrane filters used for concentration and elution or for qualitative methods. These tests are applicable to the membrane filters intended for the microbiological analysis of different types of water, such as: —    drinking water, bottled water and other types of water with expected low numbers of microorganisms; —    water with expected higher numbers of microorganisms, for example, surface water and process water. These tests are intended to demonstrate the suitability of the whole system (membrane filter together with the culture medium including the filtration step) required for the specific tests described in References [3], [6], [8], [10], [12] and [13]. This document applies to: —    manufacturers producing membrane filters; —    microbiological laboratories using membrane filters for their own testing or providing these to other end users.