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Thames Water has been using the IDEXX Colilert-18 ® testing system to detect the presence of E . coli and coliforms in drinking water , raw water and sewage cake for more than 15 years . Colilert-18 gives accurate and confirmed results in 18 hours for both E . coli and coliforms , in contrast to other tests that require a confirmation step and typically take two or three days . It also conforms to the new ISO definition of these microbes and recently became the revised ISO 9308- 2 standard . While it is more expensive than alternative tests , Thames ’ microbiology manager Stephen Bullock believes this is more than offset by the wider benefits the method brings . ‘ Colilert has been shown to pick up E . coli and coliforms in samples more accurately than alternative test methods , with negligible false positive and negatives ’ he says .

Picking up contamination earlier , before it gets out into the wider water supply and reaches customers means that operators do not have to be sent out to investigate and perform costly remediation , such as the hyperchlorination of large sections of the distribution system . False positives can lead to an operator being sent out unnecessarily . False negatives can be even more costly . If the test