How Does Tucson Water Keep My Water Safe from Bacteria?

The following provides an overview of how Tucson Water monitors for bacteria and other microorganisms and what we will do if they are found.

Why do we look for microorganisms in water?
Monitoring for microbiological contamination of drinking water supplies is necessary to determine the sanitary quality of the water. Around the world, millions of people suffer from water-borne diseases due to microorganisms in their drinking water. Here in the United States, we have few water-borne disease outbreaks because the water is very carefully monitored for disease-causing organisms. In addition, most water providers add a disinfectant to the drinking water supply to help control microorganisms which may be present.
What does Tucson Water test for?
Tucson's groundwater is pumped from deep wells and is free of disease-causing organisms, including protozoans such as Cryptosporidium and Giardia. However, it is possible for bacteria to enter the public water system once the water has been pumped from the ground. A group of bacteria known as the "coliform" group is tested for and used as an indicator of the possible presence of disease-causing organisms. Because coliform bacteria always are present in very high concentrations in the normal intestinal tract of humans and other warm-blooded animals, they tend to accompany any disease-causing bacteria which may be present in water. Monitoring coliform bacteria as an indication of water quality has been common for more than 75 years.
In addition to testing for coliforms in general, Tucson Water also looks for a specific type of coliform which grows only in the intestines of warm-blooded animals. This test is for E. coli, which provides a very specific indication of the potential for other disease-causing organisms being present in the water.
What type of testing does Tucson Water perform now?
Tucson Water collects samples at a minimum of 247 sites throughout its 11 drinking water systems each month. Special sampling points, protected from environmental contamination, are used to be sure the samples accurately reflect the drinking water system. Water samples are immediately taken to our Water Quality Laboratory. Nutrients are added and the samples are allowed to incubate for 24 hours. The samples are then checked for the presence of coliform bacteria, including a special test for E. coli.
What happens if you find coliform in the water?
If coliform bacteria are found, Tucson Water sends an analyst to the affected site to collect an additional sample for repeat testing. Samples also are taken from at least two additional sites in the same neighborhood. The water supply in the sample area is tested to determine that chlorine levels are present. If chlorine levels are low or if there is any other indication of reduced water quality, the water in the area is flushed out. Flushing serves two purposes: it helps remove sediment from the system and it distributes the chlorine.
What is the regulatory limit for coliform in drinking water?
Because bacteria are present everywhere, a single positive reading for total coliform does not mean a danger to public health exists. Large drinking water systems, such as Tucson Water's main system, must ensure no more than 5% of the samples taken in any month are positive for total coliforms. For Tucson, this means that no more than 13 positive coliform samples are allowed during a one-month period. The regulations for E. coli are more stringent. If any re-test of a site where E. coli has been found is positive for any type of coliform, Tucson Water must notify the principal radio and television stations serving Tucson within 72 hours.