To protect public health, the U.S. Environmental Protection Agency (EPA) sets drinking water standards which all public water providers must meet. Regular monitoring and testing of the water supply are required to assure that customers are provided with safe, healthy water in their homes and businesses. EPA regulations require water providers to regularly test public drinking water supplies for bacteria and other microorganisms.

Coliforms are a type of bacteria which occur widely in the environment including surface water, soil, and decaying organic matter. This group of bacteria includes the fecal coliform group which grows in the intestines of warm-blooded animals. While this group of coliform bacteria are generally not harmful in themselves, they have long been used as an indication of water quality.

Drinking water regulations require that Tucson Water collect a minimum of 242 coliform samples each month. When a water sample is tested for coliform bacteria, the results are reported as either positive or negative. A positive sample means that at least one coliform bacterium is present. This requires collection of a set of three additional samples at or near the same location in the distribution system. This sample set includes the original sample point plus an upstream and downstream sample within five water services. Sampling must continue until all repeat samples are negative. For public water systems, finding positive results for 5% or more of samples collected (including repeat samples) in any one month is a violation of the drinking water standard for coliform.

Microbiological water quality data provides the most recent monitoring results for each water quality sampling point for total coliform bacteria, E. coli bacteria, water temperature, and chlorine level.

All terms shown on this table are explained in Water Quality Terms and Definitions.

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