Bacteriological Sampling


City water quality technicians take at least 150 samples each month to ensure our water is safe. While taking samples for bacteriological testing, technicians also check total chlorine residuals. Water samples are then transported to the North Texas Municipal Water District's accredited laboratory for testing. Sample results are received the following business day. 
Data is updated on this site weekly.

Total Coliform Rule & Monitoring

Total coliforms are a group of related bacteria that are (with few exceptions) not harmful to humans. A variety of bacteria, parasites, and viruses, known as pathogens, can potentially cause health problems if humans ingest them. EPA considers total coliforms a useful indicator of other pathogens for drinking water. The Revised Total Coliform Rule (established by the Environmental Protection Agency)  requires public water systems to monitor total coliforms to determine the adequacy of water treatment and the integrity of the water distribution system. No more than 5.0% of samples can test positive for total coliform (TC-positive) in a month.

Bacteriological Sample Results

The graph below shows monthly results for all bacteriological samples. Heavy bacteria and total coliform are not a health threat by themselves since coliforms are naturally present in the environment. Samples with heavy bacteria and total coliform are used to indicate whether other potentially harmful bacteria may be present. Any sample with total coliform present must be re-tested at the same site and both upstream and downstream of the site. While there is not a legal requirement to retest locations where heavy bacteria has been identified, we voluntarily retest those locations also to ensure our water is safe. Fecal coliforms and E. coli are a health threat since these pathogens only come from human and animal fecal waste. Samples positive for fecal coliforms or E. coli result in corrective actions and possibly public notification.

Total Coliform Positive Samples

If a routine bacteria sample tests positive for total coliform, the sample is then tested for E. coli. Three repeat samples are required after a positive total coliform sample occurs: 1) sample from the original location, 2) sample within five houses upstream and 3) sample within five houses downstream. If any of the repeat samples test positive for total coliform, then the sample must be tested for E. coli. If any of the repeat samples test positive for E. coli, another set of repeat sampling is required, unless an assessment is triggered. For more information on assessments, refer to the quick reference guide.  The table below lists the City of Plano's positive total coliform samples from July 2011 to present. All positive total coliform samples are available through TCEQ's Drinking Water Watch database.