For the second time in two months, Icon Water's sewerage treatment network has been unable to cope and is discharging Canberra's effluent into the Molonglo River.
"Some discharges of partially treated effluent may still occur over the coming days as we continue to process the inflow following the heavy rainfall across the Canberra region over the recent days," the agency said in a statement.
"There is no risk to the ACT water supply as the effluent is released downstream of our water sources. ACT residents can continue to use their taps and drinking water as usual."
Canberra received 25mm of rain on Thursday, its most since August 5 when there was 43.8mm - the last time Icon allowed partially treated effluent to be discharged into the Molonglo River because the sewerage system was overwhelmed.
More rain is forecast for the weekend. The Bureau of Meteorology says there is a 95 per cent chance of rain on Saturday, most likely during the afternoon and evening. It's possible there will be 10-15mm.
The wet weather is expected to hang around through Sunday - when the bureau says there's an 80 per cent chance of rain, and likely to be 4-8mm - before clearing up early next working week.
There is, though, a high chance it returns on Wednesday and remains until next weekend.
The agency claims "the majority of effluent" discharged from the Lower Molonglo Water Quality Control Centre wastewater treatment plant on Friday continues to be fully treated and disinfected.
"Stormwater from heavy rains dilutes effluent received at the plant and increases river height and flows," it said.
However, residents on the section of the Murrumbidgee River from the junction of the Molonglo River and above Burrinjuck Reservoir are advised not to draw water from the river for either potable (drinking or food preparation) or non-potable (domestic or stock watering) purposes for the coming days.
Icon Water also advised against swimming and other bodily contact water sports in this section of the Murrumbidgee River.
Icon Water has notified the ACT and NSW Environment Protection Authorities (EPAs), ACTand NSW Health, and nearby residents affected by the discharge.
Meanwhile, a significant band of rain is bringing heavy showers, thunderstorms and strong gusts across NSW as widespread flooding continues and forecasters warn of possible landslides.
A trough tracking over NSW towards the coast was developing on Saturday and was likely to bring intense rainfall and the risk of flash flooding, the Bureau of Meteorology's Helen Kirkup said on Friday.
Six hourly rainfall totals of 30-50 millimetres are predicted in the Central Tablelands, the Hunter region and metropolitan Sydney, with isolated areas expected to receive up to 70mm.
After a soggy week in NSW, heavy falls on already saturated grounds would heighten the risk of landslides and debris falling across roads, Ms Kirkup said.
While the worst of the weather is forecast for Sydney, the Hunter region and the Central Tablelands, other areas can also expect rain.
