Wannon Water managing director Grant Green yesterday warned residents to boil their water as a "precautionary measure" after problems at the Hamilton treatment plant.

"All water used for drinking, food preparation, ice making or brushing teeth should be brought to a rolling boil and cooled before use," Mr Green said.

"Care should also be taken to avoid swallowing water while undertaking water-related activities (such as bathing or showering).

"We apologise for any inconvenience."

Increased turbidity in water supplies from southern Grampians catchment areas and drought relief bores had caused problems with the disinfection process, Wannon Water marketing and communications manager Annette Cannon said.

However, she said the problem was more visual than health-related.

"It is more of an aesthetic issue with water discolouration," she said.

"There is no E.coli or anything like that. Some residents might not notice any discolouration at all."

Ms Cannon said residents would probably have to continue boiling their water until mid-next week.

"There is no cause for panic. The water is not meeting the safe water guidelines for aesthetic levels, that's why we are urging people not to consume it."