Residents of 500 homes in North Bend’s Riverbend community no longer need to boil their water this week, after unsafe levels of E. coli bacteria were eliminated from their private water supply.

King County’s Department of Health found E. coli in a water sample taken at a Riverbend residence on Wednesday, Aug. 12. After results were tested, a warning went out to residents on Friday, Aug. 14.

The system was chlorinated, and clean results came after a test on Tuesday, Aug. 18. The boil order was lifted Thursday, Aug. 20.

Water System Manager Roger Lillejord said last week that the source of the bacteria was a mystery.

Water from the private water system’s well is clean, and nothing was found in the tanks. Lillejord said it would take a major leak in the one of the system’s eight miles of pipes to create the conditions needed for a backflow.

“It’s challenging, because there’s no evidence,” Lillejord said. “Everybody’s house is a potential source.”

Riverbend does not normally chlorinate its water, and Lillejord said that residents are typically more than satisfied with the water.

The system was built in 1982, and had a one-day contamination event in 2002.

“Prior to that, the water’s always tested well,” Lillejord said.

Water is tested twice per month in the system.

Diann Pattermann, co-owner at Cascade Golf Course in North Bend, reminded her patrons that the course and its Riverbend Cafe restaurant are on Sallal Water Association supply — not Riverbend water.

“It’s causing us a problem,” Pattermann said. “Everyone is associating Riverbend Cafe with Riverbend community.”

• E. coli bacteria are bacteria whose presence indicates that water may be contaminated with human or animal wastes. Microbes in these wastes can cause short-term effects, such as diarrhea, cramps, nausea, headaches, or other symptoms. They may pose a special health risk for infants, young children, some of the elderly, and people with severely compromised immune systems.