The 5,000 customers in King County Water District 54 still will have to boil water before using it, at least until Wednesday, after E. coli bacteria was found during a routine test.

Eric Clarke, water-district manager, said the system in Southwest King County will be flushed with chlorine Tuesday and water will be taken again from the six sites routinely sampled. The samples are placed in a petri dish to see if bacteria will grow. If the sample is clear, one more round of tests will be necessary before the order to consume only boiled water is lifted, he said.

Wednesday would be the earliest the advisory might be lifted. Until then, customers should continue to briskly boil water before use.

“It’s better to be safe than sorry,’’ Clarke said.

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Sunday, the state Department of Health ordered customers in the district to boil water used for drinking, cooking, brushing teeth and preparation of food. It also ordered the closure of all commercial kitchens in the area. Dozens of restaurants closed, along with the kitchen at Wesley Homes retirement facilities in Des Moines.

Five hundred residents at the facility, which has a nursing home as well as independent cottages, were served lunch and dinner by the Red Cross on Sunday, said Christine Tremain, Wesley’s vice president of marketing. She said the nearby Judson Park retirement complex, which is in another water district, also helped with food preparation. The local QFC provided bottled water.

“We have an emergency plan for just this kind of incident,’’ Tremain said.

The home did get permission to open the kitchen again on Monday, she said.

The affected area extends south from South 212th Street to the Kent-Des Moines Road and east from Puget Sound to 14th Avenue South, and includes parts of the cities of Des Moines and Normandy Park.

Clarke said the test that initially showed E. coli could have been contaminated by the faucet at the service connection — which is at a vacant lot where many walk their dogs, he said. He said he doubts the test indicates reservoir contamination.

E. coli bacteria can cause gastrointestinal illness.

Nancy Bartley: