The advisory affects about 2,800 residents of the lakeside development 10 miles southeast of Yelm.
On Wednesday, crews disinfected the water system. On Thursday, a state Department of Health engineer will look for the source of the contamination.
E. coli bacteria can cause gastrointestinal illness.
To kill the bacteria, customers should boil tap water they use for drinking, brushing teeth, preparing food, and washing dishes. Water should be heated to a brisk boil for one minute and then allowed to cool before using.
The boil water advisory remains in effect until the water meets the safe drinking water standards.