How are E. coli levels measured?
Daily water samples are collected from the beach each morning in sterile bottles. The samples are brought to the laboratory where they are processed for E. coli within 6 hours of collection. The method used to determine levels of E. coli is called membrane filtration. During membrane filtration, a measured amount of water is poured through a filter to trap bacteria onto the filter. The filter is placed on an agar plate and allowed to incubate at a warm temperature overnight. Colonies are counted the next day and recorded as colonies per 100 milliliters. A milliliter is a very small quantity of water—about 0.03 fluid ounces or one-fifth of a teaspoon.
