Evergreen High School was dismissed early Wednesday after a plumbing problem left 1,700 students and 200 staff members without a supply of fresh water.

After several hours, the problem was traced to a backflow connection, which is installed where the school’s water supply connects to the city’s system.

The problem was resolved and students can return to class Thursday, according to an alert from the district.

Backflow prevention devices protect drinkable water from contamination. They prevent any possibility of contaminated water flowing back into the water system.

The water went out at the campus about noon, and the district ultimately sent students home shortly after 1 p.m.