Watercare hopes to be running its Mangere treatment plant entirely on biogas by 2025.

Two major wastewater treatment plants are set to go electricity-neutral.

Watercare's plants at Mangere and Rosedale are on track to run entirely on self-generated electricity by the year 2025.

Biogas, a by-product of the wastewater treatment process, is now meeting 56 per cent of the electricity needs of the two plants.

Annually, they require enough electricity to power about 22,000 homes.

Watercare chief executive Raveen Jaduram says the council-controlled organisation is determined to meet its "ambitious" goal.

"If our Mangere plant becomes self-sufficient in terms of generating electricity, we will have achieved a world-first for a plant of its size."

Watercare has signed a three-year agreement with the Energy Efficiency and Conservation Authority, a Crown agency, to save energy and reduce carbon emissions.

The organisation's assets - including plants, networks, pump stations and offices - will be assessed to identify areas where efficiency gains can be made.

Authority chief executive Mike Underhill says Watercare's ambition and commitment is to be applauded.

"This is a massive undertaking and will place Watercare at the forefront worldwide as an energy neutral wastewater plant."