Early irrigation restrictions have helped South Canterbury's Opuha Dam reach 80 percent of its capacity.
But with little rain expected in the coming months, farmers are being warned this summer could be harder than last.
The irrigation water supply from the dam was turned off for the first time in its 17 years of operation last February as a result of the drought.
Opuha Water chief executive Tony McCormick said the dam's level was ahead of where it was this time last year because restrictions had been in place since September.
"There hasn't been the same rain and snow fall top up as last year and as El Nino strengthens, the demand for water is picking up", he said.
"The river has essentially been on restrictions right through the year in an effort by everyone to fill the dam. We got very close - to 98 percent - but now irrigation demand and a very dry catchment is leading to a draw down of the lake since early October."
Mr McCormick expected a steady drop in water levels from now.
"In a normal year we would still expect to see the periods where the lake level would rise...but I'm expecting to see very much like we saw last year where from early October it's just a steady decline. It is survival mode."
A different approach to restrictions was being tried for November, he said.
"Where as previously we restricted on a day-by-day basis...in November we've taken a different approach, where at the start of the month we advised irrigators that they had 75 percent of their monthly volume available to them and they could use that through the month and it just provided individual users with a lot more flexibility."
The company is expecting the water supply could last until the end of March.