Victoria's $6.1 billion desalination plant has passed all its tests and will finally be commissioned for use this week.
However the plant, one of the most complex infrastructure projects undertaken in Australia in recent years, will be placed on standby until the water is needed.
The plant was commissioned to provide 150 billion litres of high quality drinking water a year for Melbourne, Geelong, Westernport and Wonthaggi.
It comprises 29 buildings, two underground tunnels of more than one kilometre long each, an 84 kilometre pipeline to deliver water and an 87 kilometre underground power cable.
The plant achieved its Reliability Testing Finalisation at 5pm (AEDT) on Monday after running at maximum capacity for a month, the state government announced on Tuesday.
The testing delivered 450,000 cubic metres of drinking water to Cardinia Reservoir per day.
Water Minister Peter Walsh said the holding charge of $1.8 million a day would now begin on Tuesday and refunds would be finalised for Melbourne Water customers who were overcharged earlier this year.
A government spokeswoman said the water minister will place a water order by April 1 each year.
This year a zero order has been placed and it is yet to be seen when the first litres of water will be ordered from the plant.
The Wonthaggi plant has been plagued by controversy since its announcement by the former Bracks Labor government in June 2007.
Local residents fought against it, industrial disputes abounded and its projected cost blew out from an initial $3.1 billion to $6.1 billion.
The plant's completion date was delayed and the drought ended before its completion.
Melbourne Water users were then overcharged by $300 million before it commenced operating and this month the plant builder claimed the plant was too big.
Now with the plant finally ready for business, Melbourne dams are at 81.2 per cent, compared to a low of 25 per cent in June 2009.
AquaSure, which is overseeing the plant's construction and operation, said it had run faultlessly since testing began in mid-2012.