When cloudy and white water came out of household taps last week around Phillip Island, one online wit commented he would "expect milk to come out of a Cowes tap".

Another suggested people "just add Milo".

But Westernport Water reassured residents the milky water was the result of an upgrading project on Phillip Island Rd, near Wimbledon Heights.

A Westernport Water spokesperson said an alternative water supply line was introduced to enable upgrade works to replace a large pressure reduction valve (PRV), requiring the existing water network to be taken offline

"When charging the water pipe on Wednesday March 19, air has been trapped making the water appear milky or cloudy," the spokesperson said.

"Our team has been flushing the pipe to clear the air.  This is harmless, and the water remains safe to consume."

They said the appearance would clear once the aerated water had been flushed from the system, however, "aerated water can take up to 48 hours to clear". 

"We ask that customers who experience this, please flush their back tap until the water runs clear."

Westernport Water are upgrading the Cowes PRV at 2102 Phillip Island Road, which will increase the flow rate of water required to meet demand for the next 40 years.

"To improve safety, we're moving the entire PRV system above ground and upgrading access to the site as part of the project."

Details: westernportwater.com.au/faq-cowes-pressure-reducing-valve-prv-upgrade/