Reports say that a $99 million Sydney water recycler is sitting idle, three years after it was completed.

Fairfax Media investigations suggest that not a single tap has been turned on in the Hoxton Park Recycled Water scheme.

The big build was a major boast for NSW’s previous Labor government, designed to provide water for laundries and gardens across Sydney's booming south-west.

“This thing is just sitting there,” the Sydney Morning Herald says it was told by a Sydney Water insider.

“I think it's fair to say the taxpayer has not got value.”

It is alleged that less than half the amount of people needed for the scheme to start have signed up.

The Fairfax Media reports state that water is unlikely to begin flowing until 2018 at the earliest.

When it was first unveiled, Sydney Water announced the project had a budget of $70 million, but recent media releases value the project at $99 million.

Reports say Sydney Water has seen less demand than expected for housing in Sydney's planned south-west growth suburbs, reducing the need for the major environmental infrastructure project.

But still, money has been awarded and extensive construction undertaken, including a purpose-built treatment plant at Glenfield.

Engineering contractor John Holland performed around $40 million worth of groundwork for piping, and built large reservoirs around Hoxton Park and Edmondson, while Lend Lease laid about 21 kilometres of underground piping for the project.

“As the city continues to grow Sydney Water will continue to look at new opportunities to ease pressure on Sydney's drinking water demands,” a spokesperson for Sydney Water.