Water prices in the ACT will rise substantially in 2018 because proposed changes by the Independent Competition and Regulatory Commission have been rejected, the outgoing ICRC commissioners have said.

In their annual report, senior commissioner Malcolm Gray and commissioner Mike Buckley said they were initially optimistic about delivering policy changes on non-drinkable water, water and sewerage prices, and a greenhouse gas inventory.

But after four and a half years, they said in their report that they would leave "disappointed and frustrated" their ideas had not been taken up.

"We are disappointed and frustrated that more of this work has not been delivered the benefits to the community of the ACT that we believe it could have," they said.

"Three years after the final secondary water report was published, the ACT still lacks a holistic adaptive, strategic framework for managing its water resources.

"The most recent published water strategy document continues the piecemeal approach of its predecessors."

After a long-running stoush on water prices to secure the financial future of the new Icon Water, ACT water prices would need to increase, they said.

"The commission... is fearful that Icon Water's financial performance and profitability is likely to be less than forecast over the next few years," the report stated.

"And that water prices in the ACT will need to increase substantially in July in 2018 if Icon Water's financial future is to be secured."

ICRC 'leaner' and misunderstood: Gray and Buckley

The said in their report that the commission had been seen as "expensive" and its advice "difficult to deal with" by the Government, but in reality it had become "leaner" and was just misunderstood.

"Based on our experience... it seems to us that the nature and role of the commission is not well understood outside the commission," it read.

They urged the ACT Government to think more about how to implement proposals for change, and to discuss them with the commission before "simply responding yes or no".

"To use a buzz word of the present age, perhaps commission advice to Government could become a more interactive experience for both sides," the report said.

The terms of Mr Gray and Mr Buckley expire next February.