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Portland Water Bureau

From forest to faucet, we deliver the best drinking water in the world.


1120 SW Fifth Ave, Suite 600, Portland, OR 97204

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Bacterial Monitoring

  • Water Quality Sampling Station

    Over 210 bacterial samples are collected from dedicated stations throughout Portland's system every month.

Under the Safe Drinking Water Act, the Total Coliform Rule (TCR) requires all public water systems to test for the presence of total coliforms in the distribution system. Total coliform bacteria are (with few exceptions) not harmful to humans, and the presence of total coliforms in a water system is not considered a health risk. To determine the general health of a water system, water quality and public health agencies test for total coliforms.

In drinking water, total coliforms are measured to determine the effectiveness of water treatment throughout the distribution system. The Portland Water Bureau (PWB), like most other water providers, uses chlorine as a disinfectant to kill coliforms. We also add ammonia to form long-lasting chloramines – chloramines keep their disinfection power longer than chlorine. The presence of total coliforms tells us that this disinfection process may not be as effective as we’d like, and that our system may be vulnerable to potential contamination.

Under the TCR, the number of total coliform tests required is related to the number of people served. We are required to collect a minimum of 210 samples per month, although on average we collect about 240. We are also required to use a test that is approved by the Environmental Protection Agency (EPA) – our test provides the fastest results possible, in about 18 hours.

When total coliforms are detected, three re-samples are taken: one from the same location, one upstream, and one downstream. If these samples confirm coliforms, they can help determine the extent of their presence. According to the current TCR, if more than 5% of all the samples in any month are positive for total coliforms (with no E. coli detections), it is considered an operational deficiency and the public must be notified within 30 days. This is what happened in Southwest Portland during September and October.

Total coliform detections are not unusual in our system. The combination of lower demand and warmer water typically leads to a small increase of coliform detections in our system during the fall.

All samples that test positive for total coliforms are also tested for Escherichia coli (E. coli). The detection of E. coli in either the initial or follow-up sample is considered an indication of a serious contamination and an immediate health risk. If E. coli are detected in samples, the public is notified as soon as possible through a boil water notice.

In 2016, changes to the TCR will take effect. Since the detection of total coliforms is not a health threat, the TCR has been revised. Starting in 2016, the rule will no longer require water providers to notify the public when more than 5% of samples in a month are positive for total coliforms. Instead, the water provider will be required to perform an investigation and take steps to resolve the issue.