Officials in Longueuil issued a boil water advisory for the borough of Saint-Hubert and the neighbouring municipality of Saint-Bruno-de-Montarville.
Lab tests performed on a sample from the aqueduct system revealed the presence of the E coli bacteria in the water.
Residents should boil their water for at least a minute before using it.
Authorities are cautioning about the dangers of using unboiled water for the preparation of beverages and food, washing fruits and vegetables, making ice, and brushing teeth.
However, unboiled tap water can be used to wash dishes - assuming they are dried well - washing clothes, and taking a shower or bath.
Parents of young children and infants should consider washing them with a cloth to prevent them from swallowing water.
