A boil water order has been issued by the Joint Abington-Rockland Waterworks.
Officials say one of six repeat samples collected on Wednesday contained total coliform and E. coli bacteria.
Residents are being advised to bring all water to a rolling boil and let it boil for at least one minute or use bottled water.
In the meantime officials say a system wide sampling of all sources, treatment plants and the distribution system is being undertaken and that chlorination residuals at all treatment plant locations have been increased as a preventative measure and flushing of the distribution system will continue.
Officials say they anticipate the problem being resolved within 48-72 hours.