There Likely Was No E. Coli In Natick's Water, Inquiry Shows

NATICK, MA — The second-most concerning public health situation in Natick in recent months may have been due to a lab error, town officials believe.

On Jan. 13, Natick told residents to boil drinking water after routine tests discovered E. coli in the town's water supply. Nine of 12 water tests were positive for the bacteria, officials said at the time. The order was lifted on Jan. 15 when tests cleared the water supply.

During Wednesday's Select Board meeting, acting Town Administrator Robert Rooney reported back on an investigation into the contamination. Following the boil-water notice, the town conducted two separate system-wide tests, and both came back negative for E. coli, allowing the boil-water notice to be lifted.

The town then launched an investigation into what may have caused the tests to detect the harmful bacteria, and enlisted an independent firm to help. The conclusion: Natick's water samples may have been cross-contaminated at the Rhode Island lab where they were tested. State Department of Environmental Quality (DEQ) officials told Natick they typically see up to six false-positive test situations per year.

Rooney noted Natick has been using the Rhode Island lab, which is certified by the DEQ, for more than a decade with a good track record.

"Natick’s water system is rigorously monitored and tested with over 1,500 water quality tests performed in a DEP certified lab annually," Rooney's memo said. "Given the last recalled positive test results, this equates to a magnitude of almost 20,000 water quality samples performed without such an incident. The point being, is that the 'false positive' two weeks ago does not negate a tremendous record of a clean and dependable water service in Natick."

The boil-water advisory also affected dozens of homes in Wellesley, which shares some of Natick's water supply. There were no water-borne illnesses reported during the boil-water period.

After the boil-water notice, local public works officials speculated E. coli may have entered the system via an animal getting into the water supply, a water pipe break — or a false-positive test.