Watercare is looking at using treated water as drinking water, as Auckland faces one of its worst droughts.
Waikato University associate professor Dr Te Kahautu Maxwell said Māori would never use or consume anything to do with human discharge.
"It's not the right thing to do with Māori protocols and Māori ways of doing things right," he said.
"I don't know of any old practices of old ancient times when even human waste was used as a fertiliser on the crops."
Maxwell said Watercare should consult with iwi before going any further.