Hydro lake levels are falling and wholesale power prices rising as drought threatens in parts of the country.
The country's biggest hydro generator, Meridian, said its Lake Pukaki storage was just below average, at 94 per cent, and Lakes Manapouri and Te Anau were in the middle of the main normal range.
"We are comfortable with the current situation. As always, we are keeping a close eye on conditions," a spokesman said.
Meridian's operating report for December shows its inflows last month were 81 per cent of average.
In its main Waitaki catchment, storage dropped from 99 per cent of average to 91 per cent during the month. Inland eastern areas of the South Island have been particularly dry.
Mighty River Power said that while industry-wide national storage was 93 per cent of average, storage at Lake Taupo, which feeds its Waikato River network of stations, was above average.
Transpower has oversight of the electricity system and says that while there had been a fall in storage to below average in the South Island, the risk of shortages over the next eight to 10 weeks remains low.
A fire danger-style "risk meter" is set to normal and Transpower says the threat of a shortage in the following two to three months is largely dependent on rainfall and snow melt in hydro catchments.
In figures to the start of this week, Transpower said the spot price had averaged $78 per MWh over the past four weeks and this was higher than prices at this time last year. Latest NZX figures show prices have increased from just on $78 per MWh last Tuesday to $99 a week later.
The Meridian data shows a sharp rise in the average price it has been paid for its generation during the past six months - up 62 per cent on the comparable period last year. And after several years of falling or flat demand there was an increase in sales of 3.3 per cent in December compared with the same month in 2013. For the calendar year 2014, demand increased 1.3 per cent.
Mighty River Power will release its latest operating figures next week but general manager of hydro/wholesale Phil Gibson said the make-up of the partially listed company's portfolio, including its large geothermal base, meant it had a high level of resilience and flexibility to mitigate dry conditions.
About 40 per cent of MRP's total generation is geothermal.