Graffiti vandals struck again over the weekend, this time targeting a prominent water reservoir on Koko Head.

The large blue letters covering the structure appeared over the weekend and can be seen above Koko Head Elementary School at least a mile from the base of the mountain.

Residents reported that several public schools, including Kaimuki Middle School, Wilson Elementary School and Jefferson Elementary School, had all been recently vandalized by graffiti.

Board of Water Supply spokeswoman Su Shin said the large, often highly visible reservoirs have been targeted before and that graffiti continues to be an issue.

"It takes our crews time, money and effort to repaint those structures," she said.

"It's time spent away from doing legitimate work on the water system."

The Board of Water Supply asks residents to call 748-5000 to report graffiti and 911 to report suspicious activity around a reservoir or other structure.