A new source will supply gigalitres of water to mines in some of Australia’s harshest country.

West Australian Premier Colin Barnett has opened the $310 million Bungaroo Valley bore, which will provide 10 gigalitres-a-year to Rio Tinto's nearby operations, with some for domestic use in the towns of Wickham and Dampier.

The new bore should relieve some pressure on the Millstream aquifer, which provides much of the supply for the entire West Pilbara region.

Mr Barnett says the new bore means his Government can avoid building a desalination plant it had budgeted in 2011.

“We're broke, so $370 million on a desalination plant that wouldn't have produced a great deal of water was not an attractive solution,” he said.

“But the Government was, at the time prepared to go down that path. The towns had to have water.

“Rio Tinto has now essentially got its own water supply, so the Millstream resource is now free to be used by the Water Corporation to service the towns in the West Pilbara area.

“That's terribly important for the development Karratha, Dampier, Roebourne and so on,” the Premier said.

Rio Tinto says it will use about eight of the ten gigalitre annual supply.