Irish Water and Kildare County Council have issued a boil water notice for the area supplied by the Rathangan Public Water Supply, which will effect approximately 6,500 people.
The notice is in place for the entire public water supply following issues with the disinfection process at Rathnangan water treatment plant, which led to inadequate chlorination of the water supply.
Those affected are advised to boil water before use until further notice.
The areas affected include Rathangan, Tullylost, Ellistown, parts of Monasterevin, parts of Kildare Town and surrounding areas.
Irish Water Regional Operations Manager John O'Donoghue said: "We will continue to work closely with Kildare County Council and the HSE to monitor the supply and lift the notice as quickly as it is safe to do so and safeguard the supply for the future."