Residents have been told not to drink tap water in Yass, Murrumbateman, Bowning, and Binalong. The council said it was "unsafe".
In a Facebook statement, it said: "Recent rainfall and floods in Yass River catchment have caused problems with water treatment".
If tap water has to be used, the council advised that it should be boiled and allowed to cool.
Parents were warned about bathing infants.
"There is a potential risk if water is swallowed during washing and bathing. Parents and carers could consider a sponge bath for children as an alternative."
It advises on how to make tap water safe: "Water used for drinking or food preparation should be brought to a rolling boil to make it safe. Kettles with automatic shut off switches can do this. Water should then be allowed to cool and stored in a clean container with a lid and refrigerated."
And it recommends bottled water or cooled boiled water should be used for drinking or washing uncooked foods like salads, making ice or cleaning teeth.
Pets should not be allowed to drink tap water.
"Everyone, particularly people caring for young children, should be careful to avoid scalding, when you are heating and then cooling the water."
Yass Valley Council said it was working to fix the problem.
The quality of the water in the area was a contentious issue in the election last year.
Yass Valley Council said at the time that the water supply was "affected by water hardness, dissolved solids, high organic matter, iron and manganese; causing the varying taste and colour long experienced by local residents.
In 2020, residents were forced to boil their water before consumption, following a public health warning.
Yass Valley councillor Jasmin Jones aid the latest incident was because of "an ailing water treatment plant". The problem was that the 50-year-old plant couldn't cope with the volume of water produced in the heaviest rain.
The NSW government advise if a Boil Water Alert has been issued:
- Children and employees should not consume water, ice or drinks made with water, or raw foods rinsed with water that has not been boiled or filtered.
- When possible, parents and caregivers should provide their children with boiled or bottled water. Infant formula should be made with cooled boiled water.
- Access to drinking fountains should be restricted or turned off where possible, so that students do not drink unboiled water by mistake.
- Water should flow unrestricted to toilets and washrooms. Signs should be placed in the washrooms indicating that the water is not for drinking.
- Students and staff are advised to thoroughly wash their hands with soap and running warm tap water after using the toilet and handling food. Hands should then be dried thoroughly."
