DC Water collects over 200 samples monthly throughout the District and analyzes for coliform bacteria. The test indicates whether any coliform are present in the sample. Most coliform bacteria are not harmful to ingest (your intestines contain coliform that aid in digestion). EPA requires testing for coliforms because they can indicate the potential presence of more harmful microorganisms. If DC Water detects coliform, vigorous follow-up sampling and testing is immediately conducted to ensure no harmful microorganisms are present.

EPA allows up to five percent of the samples collected in a month to be positive for total coliform. The graph below shows the percent of monthly samples testing positive for total coliform over the past year.

As shown in the graph, DC Water consistently is below EPA's requirements regarding bacteria levels in the water. However, immune compromised people are at a greater risk in developing illness. DC Water encourages immune compromised individuals to consult with their doctor regarding extra precautions to avoid infection.

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