New tests on Mercer Island water find no E. coli

MERCER ISLAND — The latest round of tests on the water used by this affluent Seattle suburb was negative on Saturday for E. coli and total coliform. But officials are still advising people to boil their water just in case.

The health department says that no cases of E. coli illness have been reported.

Health officials collected 18 samples Friday and finished tests Saturday afternoon, but all of them were negative. Twice this week, residents of this island located in the middle of Lake Washington were told to take precautions with their tap water. That forced about 60 businesses to close. About 15 restaurants were allowed to open this weekend, but they must follow special procedures. The health department is inspecting those sites to make sure they follow the rules.

The next round of tests is being analyzed with results released on Sunday.

In addition to testing, the city sent dive teams into two large water-storage tanks on Saturday to inspect them. The crews reported that the tanks were clean, Mercer Island Police Cmdr. Leslie Burns said. They also dropped chlorine pellets into the floor of the reservoir.

Burns said they still have not identified the source of two different positive E. coli tests. For that reason, they health department is keeping restrictions in place.

The extra caution is needed because of the positive tests after the last protocols, she said.

This time last week, the health department had a positive test, Burns said. Officials said they would be clear if they had two back-to-back clear days. But days later, they had another positive test, so this time health officials changed the plan to make sure that doesn’t happen again.

“It’s concerning to them,” she said. “So now there’s a whole list of things the health department wants us to check. We’ll pull samples daily.”

It’s not clear when that process will end.