The Canterbury Regional Council is assuring farmers they will not have their water supply cut following a two-year review of resource consents in the Rakaia-Selwyn groundwater zone.
A commission appointed by the council in 2007 has given all consent-holders an annual water limit, and from September next year, some of the 532 consent-holders will be forced to stop irrigation when stream levels get too low.
Lowland farmers say that's unfair when their usage has stayed relatively low. Some say their farms will no longer be viable if irrigation has to stop when stream levels get too low.
A Leeston farmer, John Sunckell, from the Ellesmere Irrigation Society, says that while total water extraction has increased fourfold since the 1990s, lowland farmers are taking no more than before.
But the councillor for Rakaia, Angus McKay, says annual limits are necessary to ensure the sustainability of the water supply.
Mr McKay says nobody will actually lose allocation, but some consent-holders may have to change how they manage their long-term water usage.
The council says the review - the first-ever large-scale review of water consents in New Zealand - shows that water extraction in central Canterbury has reached its sustainable limit.
The holders, who are mainly farmers, will be able to seek a revised limit up to June 2015, based on three full seasons of irrigation data.
Appeals close on 19 March.