Flood-affected Western Sydney residents are being urged to conserve water as a processing plant struggles to keep up with demand.
Dirt and debris brought into the catchment by heavy rain and floods are threatening to overwhelm the plant at Orchard Hills.
The plant needs to slow down so it can deliver drinking water in line with Australian quality standards, Bernie Sheridan from Sydney Water said.
He said easing demand for drinking water would give the plant a chance to keep operating safely.
"We're asking customers in that area to do the usual things like take shorter showers, half flush on the loo, ensure washing machines are full and dishwashers are full before they do a load. If they got tank water, use it," Mr Sheridan told James Valentine on ABC Radio Sydney's Breakfast program.
"There's no compromise on the quality of the water we produce.
Despite the increased workload at the plant, drinking water coming through taps in people's homes will still be clear, Mr Sheridan said.
The conserve water warning applies to Caddens, Cambridge Gardens, Cambridge Park, Castlereagh, Claremont Meadows, Colyton, Cranebrook, Dunheved, Emu Heights, Emu Plains, Erskine Park, Glenmore Park, Jamisontown, Jordan Springs, Kingswood, Kingswood Park, Lemongrove, Leonay, Llandilo, Londonderry, Mt. Pleasant, North St. Marys, Orchard Hills, Oxley Park, Penrith, Quarry Hill, Regentville, Ropes Crossing, South Penrith, St. Clair, St. Marys, Werrington, Werrington County and Werrington Downs.
Mr Sheridan said flood-affected residents were "still free to use the water".
"But if they can just economise on the use of it we'd appreciate it," he said.
Plant still dealing with fire impact
An excess of sediment is likely causing workers to frequently backwash the filtration process to unclog it, according to University of New South Wales engineering professor Stuart Khan.
"All the time that is spent backwashing is time that the plant is not filtering water to produce drinking water," he said.
Dr Khan said the impact of the Black Summer bushfires on the Warragamba Dam's catchment may have exacerbated inflows because the destruction of vegetation made the area more prone to erosion.
"When the big rain events come, lots of sediment is washed from the catchment into the waterways and then into Warragamba Dam," he said.
Dr Khan said despite the issues facing Sydney Water, the importance of drinking water was too high to consider compromising on quality to retain the normal fast rates of production.
The area serviced by the Orchard Hills processing plant is unable to be serviced by alternative water sources because other dams had also been impacted by the flooding disaster and Sydney's desalination plant could not service the area at the moment, Dr Khan said.
He said having some spare filtration capacity at the facility could prevent the problem from recurring.
The Bureau of Meteorology said the rain had eased in the Sydney area but some flood warnings remained in place.
The rain has now moved north, impacting the state's Mid North Coast and Hunter regions.
