The company running Canterbury's Opuha Dam is hoping early irrigation restrictions will keep supply going until the end of March.
The dam is at 80 percent of its capacity and Opuha Water chief executive Tony McCormick said the supply was expected to steadily drop from now, with little rain expected in coming months.
The 250 shareholders have been on restrictions since September. Farmers are allowed to draw up to 75 percent of their supply over a month, rather than a daily limit as previously.
The demand for water is already high as the region becomes increasingly dry, but Mr McCormack said they would try to keep water available for as long as possible.
"The nature of this storage is we are always reliant on in flows to supplement the storage. Even having it full at the start of the season is never a guarantee we'll make it thought the season.
"Through modelling, we're attempting to keep an eye on when the storage may run out.
"At the moment [it is] playing through a scenario much like last year, which of course had some very hard times in it with prolonged restrictions.
The company is expecting the water supply could last until the end of March.
"Our primary aim is to maintain some level of supply right through the season," Mr McCormack said.