BOSTON -- A second Massachusetts town warned residents Friday that the water supply had been contaminated with a dangerous chemical known to cause brain damage and affect the growth of children and unborn babies.

Water samples taken in Millbury contained nearly five times the state-mandated limit of perchlorate, an inorganic chemical used widely as an oxidizing agent.

The Millbury Avenue Well, which tested positive for perchlorate, was disconnected from the town’s water supply on Friday afternoon.

A water warning was also issued in Hamilton on Saturday after the town's water supply was tainted by the chemical.

Warnings by the two towns advise pregnant women, nursing mothers and children not to drink the water. Boiling the water will not remove the perchlorate.

The water must test safe for six straight days before the warning can be lifted in either town. According to Hamilton director of public works John Tomasz, samples taken in the town Thursday and Friday both tested safe.

Tomasz said the cause of the contamination was being investigated.

The results of the most recent tests in Millbury were not available.