Microbiological Testing

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. We have few water-borne disease outbreaks in the United States because our 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.

Monitoring coliform bacteria as an indication of water quality has been common for more than 75 years. A group of bacteria known as the "coliform" group is tested and used as an indicator of the possible presence of disease-causing organisms in the distribution system. E.coli, a type of coliform bacteria, are present in very high concentrations in the normal intestinal tract of humans and other warm-blooded animals to aid in digestion. Finding E.coli provides a very specific indication that fecal bacteria and other disease-causing bacteria and viruses may have entered the distribution system.

What type of testing does Tucson Water perform now?

  • Tucson Water collects samples at a minimum of 266 sites throughout its 10 drinking water systems each month.
  • Special sampling stations that represent the water quality in the drinking water system, and are protected from environmental contamination, are tested for coliforms.
  • 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 and E. coli.

What happens if you find coliform in the water?

If coliform bacteria are found in the distribution system, a Maintenance crew is dispatched to the affected area to immediately flush the mains to bring in new water, chlorine, and remove sediments, if present. Within 24 hours, a chemist will sample ten source wells that the Environmental Scientist and Water Operations Superintendent identified as potential sources of the contaminated water. In addition, additional sites are tested in the distribution system, including the site that previously showed coliform bacteria. Flushing and testing in the distribution system is repeated until coliforms and E.coli are no longer present.

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.

Tucson Water's main system is tested monthly for coliforms. more than 13 or 5% of the samples taken in any month are positive for total coliforms, then a Level 1 assessment evaluation is triggered to identify the source of the contamination and correct the deficiency. For small drinking water systems, if more than one sample, taken in any month is positive for total coliforms, then a Level 1 assessment evaluation is triggered to identify the source of the contamination and correct the deficiency.

The regulations for E. coli are more stringent. A more serious type of assessment is triggered when a combination of total coliforms and E.coli are found in the original or repeat samples. Within 24 hours after the tests are completed, the public will be given notice to not drink the water or boil the water before drinking it. The notices will be mailed to the affected customer and posted on this website and social media within 24 hours, and will be broadcasted on television and radio.