The City of Henderson and the Franklin County Public Utilities Department on Tuesday were ordering customers to boil their water before drinking it or using it to cook or make ice.
The county agency gets its water from Henderson, and that system has low pressure because of problems with pumps at the Kerr Lake Regional Water Plant, the city said in a statement posted on its website.
The problem began on Monday, officials said.
Water should boil vigorously for one minute before being used for drinking, washing dishes, food preparation, brushing teeth and making ice, the city statement said.
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Franklin County and Henderson said the boil-water order would be in effect until the pump problems were fixed.
Water systems are vulnerable to untreated water infiltrating the pipe system when the water in the lines is not at full pressure.