Forecasters are warning a lack of rain for parts of the North Island could push the region into a "meteorological drought".
"Below normal rainfall is forecast for almost all of NZ through the end of January," a NIWA spokesperson said on Wednesday.
"Soil moisture deficits are expected to increase countrywide and some areas in the upper North Island will likely move into meteorological drought."
The forecaster said, according to its drought index, that Northland, Auckland, and northern Waikato were among the driest areas.
"With little rainfall forecast over the next 10 days, it is possible that some areas will move into meteorological drought," NIWA said on Twitter.
The Hauraki District is already seeing the impact with a total watering ban in place for Waihi and Waikino.
"River levels in Waihi and Waikino are low and we need to save water now," the Hauraki District Council said in a statement.
"The ban includes all use of water outside the house such as watering lawns and gardens, washing cars, houses and decks, filling paddling pools or playing under sprinklers.
"All other parts of the district are asked to please save water where they can."
Forecasters had expected New Zealand to enter a period of calm and dry weather.
"There are signs it may last a week, with warmer, calmer and sunnier weather for many regions," WeatherWatch said.
"It appears to be a strong, solid, high."