Frequent Questions

Public water systems that filter their water and serve fewer than 10,000 people must sample their source water for E. coli (or state-approved alternate indicator, see 40 CFR 141.701(a)(5)) or notify the State that it will monitor for Cryptosporidium rathe

To determine the annual mean, the results of all the samples for 12 months (one sample at least every two weeks) are added together. The sum is then divided by the total number of samples (Complying with the Long Term 2 Enhanced Surface Water Treatment Rule: Small Entity Compliance Guide, EPA815-R-07-015, May 2008).
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