Cochise Health and Social Services was notified Friday by the Arizona Department of Environmental Quality about a problem with the East Slope Water Company.
Routine monthly water tests confirmed the presence of E. coli bacteria in the water system.
The utility company suspects the problem occurred in a hydromatic tank, not the well itself since that is completely sealed.
Routine chlorination occurs in the hydromatic tanks and it's suspected a valve may have become stuck and allowed untreated water to pass through the tank.
Boiling water kills E. coli bacteria and coliforms.
Health officials say boiled or bottled water should be used for drinking, making ice, brushing teeth, washing dishes and food preparation.