The government today said its call for expressions of interest to build the 50-gigalitre plant had been met with strong interest.

SA Water Security Minister Karlene Maywald said the government was on track to deliver the first fresh water from the plant in December 2011 but would try to have it operating earlier if possible.

"SA Water will be asking companies which have tendered through the current expressions of interest process whether construction of the plant can be further fast-tracked," Ms Maywald said.

The minister today launched a pilot desalination plant, which is testing the technology to be used in the full-scale facility.

For the next six to 12 months the pilot plant will monitor seawater quality, assess the pre-treatment process and conduct testing of the reverse osmosis membranes.

Once complete, the full-scale plant will cost about $1.1 billion and should provide up to 25 per cent of Adelaide's water needs.

It will also be designed to be expanded in the future to supply up to half of the city's water requirements.

State Opposition Leader Martin Hamilton-Smith said the government had been dragging its heels on desalination technology for years.

"We should be having a ceremony today to cut the ribbon on a desalination plant - not a pilot plant," Mr Hamilton-Smith said.

"South Australia is in the midst of a water crisis and Premier (Mike) Rann won't deliver a working desalination plant until at least 2012.

"The government has so far been dragging its heels on desalination and praying for rain."