Irrigation NZ CEO Andrew Curtis says comparing human and farm use of water does not make sense - farms occupy a much larger land area and produce something from the water they use - for example a 100-hectare crop of wheat produces enough bread to feed 10,000 families for a year.
He disagrees with the assertions made by former Treasury economist Peter Fraser who said that (according to his statistics), one farmer can use as much water as 30,000 city dwellers.
"Mr Fraser is wrong to say that irrigation uses 78 percent of water. Irrigation actually uses 62 percent of water according to the most recent data from Land and Water Aotearoa. These figures exclude hydro-electric use - if hydro use is included, irrigation use is a much lower proportion of total use," he says.
"If we didn't have irrigation, New Zealanders would not have access to such a range of quality local food at an affordable price."
The Labour Party has proposed a tax on irrigators of one to two cents per litre to pay for the cost of cleaning up the nation's rivers.
National has claimed the tax would lead to hugely increased costs for farmers and open up possible new treaty claims at the Waitangi Tribunal.