The Commerce Commission says it is tightening its scrutiny on Wellington's new water entity Tiaki Wai.

And it says the relevant minister is separately considering more rules about the organisation's performance.

In a decision released on Wednesday, the commission said the new measures will require Tiaki Wai to provide more detailed reporting including on fixing faults, and maintenance spending.

The requirements will mean independent experts will scrutinise the entity's spending plans in a bid to ensure value for money.

The Commission said Commerce and Consumer Affairs Minister Cameron Brewer was considering imposing performance requirement rules on Tiaki Wai.

Tiaki Wai has faced criticism since it took over the region's water assets, with some residents confused about the size of water bills in relation to council rates, and questioning why they have received bills for car parks, granny flats or flood-damaged homes they cannotlive in.

Water bills will on average increase by 13.3 percent for Wellington residents this financial year, and are projected to cost on average $6208 in a decade.

Commerce Commission chair John Small said the new rules would give residents and councils more transparency of spending, how services are performing and whether improvements are being made.

Facing higher bills, Small said households needed to be sure money was "being spent wisely".

"Consumers want confidence that investment is being directed to the right priorities and that promised improvements are being delivered. We will take an active role in monitoring Tiaki Wai's performance, closely review the information it reports, and focus our efforts where greater oversight can have the biggest impact."

Leaders at Tiaki Wai have said it will cost $25 billion over the next three decades to fix the city's failing water infrastructure, deliver a safe water supply and keep harbours and beaches clean.

In a statement, Tiaki Wai board chair Will Peet said the new rules would not resolve the challenges facing the organisation, but were part of a plan to restore the network and build trust.

"We have been open from the start that prices will need to rise to address historic underinvestment - that is already reflected in our Water Services Strategy."

Peet said a second water strategy would provide more details on future spending.

"It's natural our customers want to know what's going on, how decisions are being made and that their money is being well spent. We welcome this decision from the Commission because it helps to provide that certainty for communities."

Wellington Mayor Andrew Little said he was pleased the Commerce Commission and central government had agreed to stronger oversight.

But he said it did not go far enough, when it stopped short of full "price quality" regulation.

"The next step is the central government must act to implement price quality regulation for Tiaki Wai, so Wellingtonians can have confidence prices will be fair while the pipes are being fixed."