The council said in a statement on March 13 that recent heavy rainfall in the Glenbawn Dam catchment had caused problems with effective water treatment, making drinking water in the Scone and Murrurundi water supply systems potentially unsafe.

Water supplied to Aberdeen, Merriwa and Cassilis is unaffected.

"We ask residents not to be alarmed, this action to boil all drinking water is a proactive and preventative measure to manage the risk and ensure the safety of residents," the statement said.

Recent rainfall has caused algae to form in Glenbawn Dam.

While levels are relatively low, it still constitutes an 'amber' status as per the NSW Algal Advisory Group Guidelines, and WaterNSW (the dam operators) respond to this status by switching to the lowest level water offtake - in order to supply water that has the least chance to contain algae.

However, switching raw water supply to the low-level offtake has resulted in a steady increase in turbidity in the water.

Based on the latest water quality results from the Scone water supply system, the turbidity is now too high to adequately guarantee the safety of the water for human consumption.

This does not mean the water is unsafe - only that the risk of it being unsafe is too high.

Based on NSW Health advice, Upper Hunter Shire Council have issued a boiled water alert.

"Water used for drinking or food preparation should be brought to a rolling boil to make it safe," the statement continued.

"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.

"Bottled water or cool boiled water should be used for drinking, washing uncooked food (e.g. salad vegetables and fruit), making ice, cleaning teeth, gargling and pet's drinking water.

"Dishes should be washed in hot soapy water or in a dishwasher.

"Children should take bottled water or cool boiled water to school.

"If you cannot boil the water, unscented household bleach (containing 4 per cent - 5 per cent available chlorine) may be used.

"Add two drops of bleach to 1 litre of water (or 4 drops if the water is cloudy), mix well, and allow to stand for 30 minutes before use."

This advice should be followed until further notice while Upper Hunter Shire Council works to fix the problem.

For more information, visit the NSW Health website: https://www.health.nsw.gov.au/environm.../.../Pages/default.aspx