The town's water system was found in violation of a state Department of Environmental Protection standard in June, when a test of the public supply turned up coliform bacteria, which are found in water, soil, vegetation, and in large quantities in animal feces. Nine of 91 samples contained the bacteria, which typically do not trigger serious illness, but can indicate other organisms of fecal origin, such as E. coli. Follow-up testing did not find E. coli or other troubling fecal bacteria, according to the Water Department. Residents do not need to boil water, but individuals with severely compromised immune systems, infants, and the elderly may be at risk of infection and should seek medical counsel, according to an alert on the town’s website, www.town.canton.ma.us.