Opponents of a proposed water treatment plant in west Auckland now have the support of the deputy prime minister.

Council-owned water company Watercare is considering taking over 12 to 18 properties in Oratia, to build a replacement to the 90-year-old Huia water treatment plant.

Paula Bennett has been living in Oratia for the last eight years, and is now coming out publicly against the proposal.

The deputy prime minister said she is not allowed to interfere in Watercare's decision, as she has a conflict of interest as a local citizen.

But she told hundreds of local residents at a public meeting last night that she does not want the proposal to go ahead.

"This is personal. It's not just about those whose homes will be taken. I am a resident of this community. It is about all of us.

"This is my community as well and I don't want to see Watercare tearing the heart out of our local community.

"It's not just a few people. It is more than that - it is everything it is too us... our families, our homes."

Bennett said she is voicing her concerns as a private citizen, but she will also be closely monitoring the process as a local politician.

"This is a council and Watercare process. This is not central Government. They didn't initiate it. It's not being done by them.

"I will make sure the process is being followed. I think this place is the wrong choice."

Auckland mayor Phil Goff said legislation also prevents him from interfering in the decisions of Watercare, as a council-controlled organisation.

However, he said the proposal would need the approval of independent hearings commissioners and could be appealed through the Environment Court.

He said he appreciates the "strength of opinion" against the proposal, and he has urged Watercare to take the concerns of locals seriously.

Watercare chief executive Raveen Jaduram said community opposition will be seriously considered.

He said a recommendation will be put to the Watercare board next month, which will include information they have received during the consultation process.

He told locals "the most powerful bit we've got back is from your community, about what you feel" about the proposal.

The meeting is likely to take place on May 29.