Mattapoisett’s Water Department has sent out letters to the town’s water users notifying them that coliform bacteria was found in the drinking supply.

Mailed on June 28, the notice stressed that the bacteria does not pose any immediate health threat and that residents do not need to boil their water or take any other action.

Four water samples taken on June 18 tested positive for the naturally occurring bacteria. The samples were taken at the eastern end of town. Though not particularly harmful, coliforms are used to indicate that other, more harmful bacteria may be present. State drinking water standards dictate that no more than one sample per month may test positive for the bacteria.

According to Water and Sewer Commissioner Nick Nicholson the town increased the chlorine dosage, chlorinated one town well, flushed a water main in the affected area and took other corrective measures.

Two days after the samples tested positive the system was clean as subsequent tests came back negative for the bacteria.

Nicholson said he was unsure how the bacteria got into the system. He noted this is the first time in 16 years town water tested positive for coliform.

“We just don’t know. We’ve been pulling our hair out trying to figure out why. It’s hard to say what it was all about,” Nicholson said.

Every month, the department takes at least 12 water samples from the supply to test. Had a more dangerous bacteria, such as fecal coliform, or E. coli, been detected residents would have been notified immediately through radio and television ads, Nicholson said.

“Fortunately, it’s not that serious of a problem,” Nicholson said.

For more information, the public may contact Nicholson at 508-758-4161 ext. 202.