Please find the link for the following US EPA
Method 1600: Enterococci in Water by Membrane Filtration Using membrane-Enterococcus Indoxyl-B-D-Glucoside Agar (mEI)
Summary - The MF method provides a direct count of bacteria in water based on the development of colonies on the surface of the membrane filter (Reference 18.5). A water sample is filtered through the membrane which retains the bacteria. Following filtration, the membrane containing the bacterial cells is placed on a selective medium, mEI agar, and incubated for 24 h at 41°C. All colonies (regardless of color) with a blue halo are recorded as enterococci colonies. Magnification and a small fluorescent lamp are used for counting to give maximum visibility of colonies.