The board directed Water Director David Craddick this past week to ask state health officials about possible side effects of having zinc orthophosphate in drinking water.
The chemical known as C-9 was introduced in June 2001 to combat excessive levels of lead, which apparently was being leached out of pipes and fittings. C-9 binds with the metals in pipes to prevent further leaching.
A number of Upcountry residents believe they developed skin irritation from the C-9 in their tap water.
Board member Virginia Parsons said her husband, Dale, suffered from a mysterious skin irritation that went away when they spent time away from their home in Makawao.
Excessive levels of lead found in water taken from the taps of Upcountry homes led to the introduction of C-9, according to Don Yasutake, an environmental engineer with the Safe Drinking Water Branch of the Health Department.
After the county began using the chemical, the water in Upcountry homes tested below the "action level" for lead contamination, he said.