About 700 properties in Alfriston, Berwick, Wilmington, Laughton, and surrounding areas are experiencing no water or low pressure, according to South East Water.
It comes as the area suffers from severe flooding following recent bad weather.
A statement from the supplier reads: “Heavy rainfall and flooding have resulted in technical problems at one of our water treatment works, which supplies the area.
“Our teams have been working around the clock to restore supplies to as many people as possible and continue working today.”
“Due to the flooding and rainfall's impact on our water treatment works, we don't anticipate normal supplies to be restored until tomorrow (Thursday, February 29).”