The drinking water supplied to Waiahole Valley has tested positive for the E. coli bacteria.

The Department of Health on Thursday notified residents, businesses and Waiahole Elementary School once the water purveyor confirmed its second positive results and instructed them to boil the water before use.

“It is very rare,” said DOH spokeswoman Janice Okubo, who recalls an incident several years ago.

The Centers for Disease Control says on its website that most strains of E. coli are harmless, while others can cause diarrhea, urinary tract infections, respiratory illness and pneumonia, and other illnesses.

Unlike most Oahu communities, Waiahole Valley is supplied with water by the Hawaii Housing Finance and Development Corp., a state agency, and the water supply is limited to that area.

Okubo said the initial sample was taken Tuesday and came back positive Wednesday. The Health Department requires a second test, which came back positive Thursday. That’s when DOH must notify the community.

Hawaii Housing will keep testing until it gets normal results, and DOH will announce it.

Hawaii Housing could not be reached for comment.

A Department of Education spokeswoman said Waiahole Elementary will have all breakfast and lunch preparation done at nearby Kahaluu Elementary School until water has returned to a safe level for consumption.

Parents are asked to supply their children with water flasks or bottled water.

The Board of Water Supply and Castle High School will provide water coolers to Waiahole Elementary.

Water stations will be set up on campus for students to refill their flasks and bottles.

The school also will provide waterless hand sanitizers on campus and in restrooms.

Waiahole Poi Factory head manager Joshua Wilson said once the company learned of the test results Thursday, “we closed immediately.”

“It’s never happened before,” he said. “There have been cases of pollution of the stream, but it’s never been the drinking water.”