The boil water advisory that has had Kent County Water Authority customers wary of tap water for three days and has had some public officials demanding more speedy notification was lifted by the Health Department shortly after 12:30 p.m. yesterday.

The system serving 29,000 customers, including about 3,900 in Warwick, tested negative for E. Coli coliform bacteria for three consecutive days. The bacteria were first found in a test sample from one of the authority’s six storage tanks on Sept. 17. The presence of E. Coli, which is often associated with animal and human waste, was established on Sunday, Sept. 22, and the authority issued a press release that afternoon of the boil water advisory. The source of the bacteria remained a mystery yesterday.

Authority manager Timothy Brown said the storage tank that has been isolated from the system is “contaminated in our eyes” and would not be brought back online until drained, cleaned and disinfected. Two tests from the tank were positive for E. Coli. No tests from outside of the tank came back positive.

“It is best to be ever vigilant,” Brown said when asked what has been learned from the experience. “We will continue to test [storage tanks] monthly. It has probably prevented a more serious outbreak down the road.”

As for the source of the bacteria, Brown didn’t venture to guess. He said the hatch on the tank was fully secured and that the fine wire mesh on the tank vent was in place.

“It is a mystery to us how this happened,” he said.

On Monday a diver was sent into the tank. Nothing out of the ordinary was found.

The positive test had other authority employees equally mystified.

“It was a fluke, but we have to treat the worse case scenario,” said Stephen Correia, one of 30 on the authority staff. He was delighted with the latest test results. “It’s absolutely clean, quality water,” he added.

With the exception of the Oaklawn neighborhood in Cranston, virtually all of the authority’s customers were advised to boil water for at least a minute before drinking it or using it to brush their teeth. The authority and Health Department also advised the affected customers not to use the water to bathe infants or to permit children to use it as they might ingest it. Those in food preparation were advised to use bottled or boiled water.

There are no known instances of people becoming ill from Kent County water.

Warwick customers impacted by the advisory were generally west and south of Apponaug. That’s an area including East Greenwich and the Potowomut section of Warwick as well as West Warwick and Coventry. Bottled water was provided by the School Department to the six Warwick schools serviced by Kent County. The same measure was taken at Kent Hospital as they dipped into the stockpile of bottled water they keep on hand.

Brown said the authority followed regulations in notifying the public within 24 hours of the advisory.

“We were well ahead of the requirement,” he said.

Nonetheless, many officials, including Mayor Scott Avedisian, felt notification should have been faster.

“It was impossible [given the authority’s existing systems] to get it out any faster,” Brown said.

That could change. Within a half hour of the advisory being lifted, Brown said the authority would test a system alerting 8,400 customers that it is safe to drink the water. He said the authority would explore implementing a system like Warwick’s CodeRED. Warwick Emergency Management used the system to notify registered residents of the boil water advisory. The notification system was also used yesterday to inform people of safe drinking water.

The notice said the authority would continue to follow test protocols and is properly monitoring the system to comply with Department of Health and EPA regulations. It goes on to apologize for the burden, inconvenience and disruption caused by the advisory.

Brown said that the two million-gallon storage tank, which held water the authority bought from the Providence Water Supply Board, would be drained slowly. He said it would not be brought back into service until all EPA and health protocols are met.