The Gilbert Public Works director has retired and the water director has been dismissed after the town began investigating why one of its water treatment plants failed to fluoridate the water.

Jennifer Alvarez, a Gilbert spokeswoman, said Lonnie Frost and Chris Ochs were placed on leave after it was discovered last month that the Northern Water Treatment Plant, which treats the water for the northern part of the town, had not fluoridated the water for 13 months.

Ochs, who had worked for the town since February 2010, has been offered a letter of dismissal, Alvarez said in a press release Thursday.

“Mark Horn will serve as the Interim Public Works Director while a national search is conducted,” Alvarez said in a press release.

Mark Horn is the current waste water manager and has been the acting public works director since Aug. 23.

The town’s water has been safe to drink, officials said. Fluoride is used to prevent tooth decay in children and adults.

In 2000, 54 percent of residents voted to add fluoride to drinking water, according to a Tribune article from 2003.

Gilbert began fluoridating the water in March 2002, according to the Centers for Disease Control.