Drinking water from Victoria's $5.7 billion desalination plant will begin trickling into Melbourne's supply in the next week, with quality tests under way, the state government says.

Water Minister Peter Walsh says the first tests have begun at the plant to ensure water being produced during the commissioning phase meets strict quality standards.

The Wonthaggi desalination plant. Credit:Craig Abraham

The next step will be to test the water's transfer along the pipeline from the plant at Wonthaggi to a Melbourne dam.

"As part of that process, desalinated water is expected to gradually enter Cardinia Reservoir in the next week or so, depending on (contractor) AquaSure's commissioning progress," Mr Walsh said in a statement.