A helicopter lifts a ResMix system into position at Cotter Dam.

A helicopter lifts a ResMix system into position at Cotter Dam. Photo: Jeffrey Chan

Canberra has a big new dam but that does not mean the city can stop thinking about conserving water.

The extended Cotter Dam has a capacity of 78 gigalitres. But under the Murray-Darling Basin Plan, the ACT is generally limited to using a maximum net figure of 40.5 gigalitres of water per year.

ACT Environment and Sustainable Development Minister Simon Corbell said the territory could buy additional entitlements to use water if necessary.

The Cotter Dam.

The Cotter Dam. Photo: Jeffrey Chan

However the ACT would probably be able to work within the cap for at least a couple of decades.

''ACTEW has already purchased certain high-security water entitlements which give them a buffer in drought,'' Mr Corbell said.

''When we're not accessing those entitlements we can actively sell them to other users on a short-term basis and that's what they've been doing,'' he said.

''The Cotter Dam would be the first point that we would go to release more water with the purchase of further entitlements above our [sustainable diversion limit].''

Additional water could also be sourced from the Murrumbidgee via the Murrumbidgee to Googong water transfer pipeline at Angle Crossing.

The government last month released a draft water strategy for public consultation.

Mr Corbell said the ACT was lucky to be the only Murray-Darling jurisdiction with a water diversion limit based on net, instead of gross, usage.

"'Net' is what we take out of the system, less what we put back into the system,'' he said.

''We're the only jurisdiction that has our SDL calculated on a net basis. The reason for that is that we're basically a closed loop in that a lot of our water ends up back in the system through the Lower Molonglo Water Treatment Plant.''

Mr Corbell said residential and non-residential water consumption had been falling in the ACT since the late 1990s.

Average consumption fell from 214 kilolitres in 1997-98 to a low of 100 kilolitres in 2010-11.

Mr Corbell believed Canberra residents would continue using water wisely.

"I think Canberrans do understand that we live in a water vulnerable part of Australia and we need to be wise about how we use water,'' he said.

Completion of projects to secure drinking water supplies had allowed planners to concentrate on improving the quality of local waterways, as reflected in the draft plan.

''The water quality in our lakes and creeks, in our urban ponds and dams, the development of an integrated catchment management approach is really the highest priority of this strategy because we need to improve the co-ordination across different areas of responsibility,'' Mr Corbell said.

This included improving co-ordination between the ACT, the National Capital Authority and NSW.

The federal government had previously given in-principle approval to the provision of $85 million to the ACT to clean up local waterways.

Mr Corbell said a business case for the project had been sent to the Commonwealth earlier this year but final approval was yet to be granted.

Feedback on the draft water plan will be accepted until the end of August.

The plan can be viewed online at timetotalk.act.gov.au.