Residents in Upper Allen Township should boil their water until further notice after E. coli bacteria was found in the water supply this week.
Suez Water announced the boil order Friday and officials said customers in the Center Square Water System were being notified about the problem through phone messages.
Residents in affected areas should not drink the water or use it for food preparation without boiling it first.
E coli bacteria can make people sick and pose additional risks for the young, old and people with weakened immune systems.
A sample collected Tuesday at a water sample station tested positive for E. coli and additional samples collected Thursday showed a "total coliform positive sample."
Tests at residential customer locations "showed no total coliform or E. coli," according to the Suez announcement.
"We are also conducting a thorough investigation to determine the source of the contamination and will implement corrective action," the statement said.
An announcement on the Suez website said bacterial contamination can occur when increased runoff enters the drinking water source.
It can also happen due to a break in the distribution pipes or a failure in the water treatment process.
The Center Square Water System includes the following streets: Atland Drive Bauman Court Beilman Court Brunswick Avenue Buckingham Avenue Cocklin Court Cope Drive, North Cope Drive, South Derbyshire Avenue Emily Drive Fenwick Avenue Fleming Drive Foribunda Lane Glime Drive Granada Lane Grandia Floria Drive Grantham Road Gregor Court Hawthorne Avenue Herman Drive Kower Court Kower Drive Lancelot Avenue Lobach Drive Merrimac Avenue Norfolk Court Paul Circle Rosegarden Blvd., East Rosegarden Blvd., North Rosegarden Blvd., South Rosegarden Blvd., West Sheffield Ave Shoff Court Stumpstown Road West Lisburn Road Wakefield Avenue White Dawn Lane