Coliform bacteria was recently detected in the city's municipal water system but residents do not need to boil their water, according to a notice sent to Waltham residents and posted on the city's website.
According to the letter, the bacteria, which naturally appears in water, was detected in water samples taken in August at levels that violate drinking water standards. The bacteria itself is not harmful.
Testing for other possible contaminants such as E. Coli and fecal coliform was negative, according to the letter.
Residents with weak immune systems or specific health should consult their doctors, according to the notice. Elderly residents are at a higher risk.
A water main break or construction on Smith Street could have caused the issue, according to the letter. The city is flushing the pipes to resolve the matter and hopes to fix it within two weeks.