Councils across New Zealand are asking people to voluntarily save water to avoid hose bans as restrictions bite across large swathes of the country.
The warnings come as meteorologists say parts of the country could be on the verge of drought.
The hot weather will continue today and tomorrow, and rain is not expected in the North Island until the weekend.
The MetService said a high pressure system would cover most of the country until Thursday, before a front from the Tasman Sea brings rain to the lower South Island.
By the end of the weekend the front is expected to move across the North Island - but it will be weakening and rain is likely to be patchy.
The next rain is likely to be on the West Coast next Thursday or Friday, according to Weatherwatch.co.nz.
The forecaster said parts of New Zealand were becoming "exceptionally dry".
"Unless something major changes in New Zealand's weather patterns, droughts may very well form in parts of the country, especially the east, as we head into 2018."
Weatherwatch said the summer could see pockets of big dry mixed with deluges. "The warmer than usual sea temperatures around the country can help create rain and La Nina can produce more tropical lows."
Most of New Zealand's land mass has been experiencing temperatures more than 8C hotter than average. Coastal regions are at least 4C above normal, and Niwa is predicting hotter-than-normal temperatures across the country until the end of February.
The northern North Island will likely get more rain than normal this summer, and the east of the South Island may be drier than normal, Niwa said.
The dry and heat across the country has hit water reservoirs as people fill pools and water their gardens.
Napier City Council, which on Monday feared it was running out of water, has eased restrictions thanks to an "overwhelmingly positive response" from the public allowing reservoirs to refill.
Hoses can now be used on alternate days in the morning and evening. Similar restrictions are in place in Palmerston North, Waikato, Taranaki, Wellington and parts of the South Island.
Other councils are preemptively asking locals to save water, including Auckland, Christchurch, Westland and Queenstown, to avoid more dire action later in the summer.
Whangarei Cloudy periods, easterlies. High 24C, Overnight 17C
Auckland Fine, easterly breezes. High 25C, Overnight 16C
Hamilton Fine, light winds. High 28C, Overnight 14C
Tauranga Mainly fine, cloud at night. Light winds. High 24C, Overnight 17C
Napier Fine, chance light shower in evening. High 25C, Overnight 17C
Wellington Cloud then mainly fine, southerlies. High 24C, Overnight 14C
Christchurch Mostly sunny with evening cloud. High 22C, Overnight 15C
Timaru Morning and evening cloud, otherwise long fine spells. High 20C, 14C
Dunedin Mostly cloudy, but afternoon fine breaks. Chance morning shower. High 20C, Overnight 16C