How often does the PWB sample for E. Coli?
The Total Coliform rule requires drinking water providers to regularly sample for coliforms—a type of bacteria in the water distribution system. Samples are tested for both total coliforms and E.coli bacteria. The number of samples is determined by the size of the population served. For Portland, this results in a minimum of 210 samples per month. These samples are collected in accordance with a State approved sampling plan. The PWB sampling plan samples throughout the distribution system based on 5 zones of similar conditions, these are determined by the infrastructure of each zone, such as downstream of Washington park reservoirs. Each zone is sampled at least 2 times per week with a goal of sampling 324 samples a month. Portland’s open reservoirs are sampled 4 days a week.
