Watercare is working to shore up the Auckland water supply well into the future

It's opened a third reservoir at the Redoubt complex in Totara Park.

The 60-million dollar project increases capacity for treated water by 45-million litres or 18 Olympic sized swimming pools.

Watercare project Manager Martin Hughes says it's a good failsafe.

He says if there are problems at Ardmore or the Waikato treatment plant then there will be breathing room for the water supply.