GWMWater has assured Horsham and Natimuk residents they will continue to be supplied with potable water after a bushfire damaged the Wartook catchment.
Managing director Mark Williams said although further assessments were to be done, it appeared the standard of water was still good enough for drinking.
"Despite the damage, an initial assessment of Lake Wartook indicates that water quality in the lake has been relatively unaffected at this stage," he said.
Vegetation was extensively burnt along parts of the transfer channel between Lake Wartook and the Mt Zero water treatment plant. GWMWater will inspect the channel when access is granted.
"We expect there might be a significant amount of debris in the channel that will need to be removed," Mr Williams said. "We are confident that the treatment plant will continue to supply our Horsham and Natimuk customers with drinking quality water."
GWMWater has approved Halls Gap's water supply as safe to drink.
A notice to boil all water had been in place from January 17 after Halls Gap's water supply was switched in an effort to have the maximum amount of water to fight bushfires.
A boil notice remained in place for Pomonal and residents north-east of the Ararat-Halls Gap Road and Grampians Road junction at the weekend. Residents were originally told bottled water would be supplied as an alternative but a GWMWater spokeswoman said not enough was able to be sourced.
A water trailer set up in Halls Gap was moved to Pomonal on Friday. Water in Pomonal should be brought to a rolling boil for one minute.