Authorities in Wellington and Hamilton say dry conditions are causing unprecedented drops in metropolitan water supplies.
Water restrictions have been put in place in both centres, along with Hastings, New Plymouth, Tasman, Invercargill, and the Buller District.
Wellington Regional Council has invoked emergency measures to take extra water from the Hutt River, which is running at 25% of its normal flow.
The chair of the council's water supply committee, Nigel Wilson, says households need to cut water use by a further 10%.
"We're looking at a situation in Wellington, as in much of the rest of the country, where you just throw the record books away. This is all completely new territory for everybody," he says.
Scientists say the risk of drought in many parts of the country is likely to double by 2040, due to climate change.
The water manager for Hamilton City Council, Tim Harty, says there is already evidence of drier weather.
He says 2008 was very dry and there has been a trend since then towards warmer, drier, longer summers.
For the first time ever, the Waikato region has reached its second highest water alert.
Mr Harty says his council has imposed sprinkler bans across the city, while Mr Wilson says Wellington intends to introduce a total outdoor water use ban if there's no rain before the weekend.
Both councils say they plan to improve water storage and supply infrastructure in the future.
Auckland's water agency Watercare says its supply is secure despite the extremely dry conditions.
Auckland's supply comes from the Waikato River, the Onehunga aquifer and dams in the Hunua and Waitakere ranges.
Watercare spokesperson Mark Champion says the company has been planning for a drought situation as well as population growth for a number of years.
He says the supply has been kept strong by investment in the extraction and processing of water from the Waikato River.
However, Mr Champion says people in Auckland should still use water wisely.
Jobs cut as river dries up
About 50 whitewater rafting guides are out of a job in Rotorua because the Kaituna River is too shallow to raft on.
River Rats rafting company co-owner Steve McNab says Bay of Plenty Regional Council decided to restrict the flow of the Kaituna on Tuesday night in response to the dry conditions throughout the region.
Mr McNab says that makes it no longer possible to raft safely on the river.
However, he says despite the drought, rafting conditions have been better than in the previous two summers, when the river was closed by flooding for several weeks.