The Cook Islands opposition Democratic Party says the government has to make public its report into the troubled water system upgrade on Rarotonga.
Te Mato Vai has been underway for more than four years and parliament has just agreed to up the Cooks commitment to meet a 50 percent cost over run.
The Democratic Party also alleges the system, being built by the China Civil Engineering Construction Company, has been using inferior materials.
The government has said the cost over run has to be expected given the time lag on the project but Democratic Party leader, Terepai Maoate, says it has to be transparent and release the inquiry report.
"We've supported - we had to put it through parliament to support the increase. Not that we wanted to. I really feel that before we go any further, it could by the sound of it, we may end up going [for] a lot more than 50 percent - extra $30 million on top of the $60 million, I for one and a lot of people in the Cook Islands do not want to end up paying some debt where we find we may have to rebuild the whole programme."
Initially Te Mato Vai has been funded through a soft loan from China of $NZ25 million, an aid grant from New Zealand of $NZ15 million, and the balance from the Cook Islands Government.
More money is expected from both the aid donors to help cover the additional costs.