Phil Hartridge, of the Tararua Economic Impact society, addressed the council in a public forum.
He said the society had been working behind the council, gathering as much information as it could.
"As an organisation we are very heartened and pleased by the way Tararua District Council is conducting the matter so far," he told councillors.
He said he encouraged the council to join with the other councils.
He also encouraged them to join with other societies considering the legal challenge,
"so we can all be informed and give as much support to those societies as we can".
Mayor Tracey Collis said the council had entered the process of Three Waters reform in good faith and had committed to engaging with the community.
She said the mandate had caused much division in the community and created further uncertainty for people and businesses during Covid.
Councillors had two options, she said.
"The first one, in my mind, is to let our communities heal after the Government's decision because it's out of our hands."
The Government had given direction on the next steps and how the council could take part in that process.
Collis said there was Covid in the community and right now that needed to be the focus.
The council's second choice was to invest and join as a Partner Council, which would give time to explore options.
Councillor Shirley Hull said this wasn't just about Three Waters.
"This is actually about democracy.
"I think our voice needs to be loud and clear back to the Government as a group that we are responding to our communities when we sign that Memorandum of Understanding on behalf of our communities."
She said she had a lot of people behind her who were concerned about the lack of democratic nature of the decision to mandate.
Councillor Peter Johns said the more people who stood up and protested the way it had been done, the better.
He said the most important thing for him was "the loss of control in our own destiny".
His concern was that decisions were made by some faceless person or committee in Nelson or Wellington and that person would make decisions on priorities.
"It could be that Nelson's requirements are greater than ours.
"No, we can't have extra water in Woodville or Pahiatua and therefore we can't grow, we can't bring in new industry that may require a degree of additional water."
Councillor Sharon Wards said it was heartening to hear the public's comments.
She said without the community support there would have been potential for the council to not have any power over the Three Waters situation.
She was also heartened to hear that the oversight group that would be part of the Memorandum of Understanding was well representative of rural communities across New Zealand.
Councillors supported signing the memorandum.
