The communities under the advisory are Ridgewood, Glen Rock and portions of Wyckoff and Midland Park.
The alert will be in place until testing shows the water is clean.
Officials say residents should not drink tap water and should wash dishes, fruits and vegetables in boiled water. They are urged not to use ice recently made from tap water. Residents should brush their teeth with boiled or bottled water and should not use tap water to make drinks. Cooking should be done with tap water only if it is boiled. Boiling for at least 1 minute will kill most organisms.
Washing hands and bathing can still be done with tap water.