Residents in Sydney’s south-west have been asked to avoid using dishwashers and washing machines to conserve drinking water supplies after heavy storms forced the shutdown of a major filtration plant.

People living in Campbelltown, Narellan, Prestons, Macarthur and Camden areas should hold off non-essential water use, Sydney Water said.

"We're basically asking customers to be conservative in their water use for the next 24 hours," Peter Hadfield, a spokesman for Sydney Water said just after 4.45 pm.

Earlier, Sydney Water blamed heavy rain in recent days for putting"enormous pressure on the Macarthur Filtration Plant, with high levels of debris and turbulence in the catchment's water".

Bernie Sheridan, Sydney Water's treatment manager, said a succession of storms in recent days had triggered a release of silt into the Cataract Dam, reducing the quality of water reaching the plant. The water authority is currently spilling the dam to help reduce turbidity.