Authorities are enforcing a complete fire ban in Gisborne and urging locals to conserve water after a broken pipe cut the city's main supply.
A pipe from the reservoir at Mangapoike, south of Gisborne, burst on Monday night following a 70-metre-long hillside slip. The district council says it could take up to two weeks to repair.
Drastic water restrictions are being implemented - including a ban on the use of water for washing cars, watering gardens and filling swimming pools.
The council has also moved to implement a total fire ban in the North Island city on Wednesday to protect the supply for firefighters.
Gisborne will run out of water in three days unless residents don't cut water use from 23,000 cubic metres a day to at least 14,000 cubic metres.
The council says water temporarily coming from the Te Arai catchment and the Waipaoa River is meeting just two-thirds of normal demand and has asked residents to voluntarily reduce consumption.
It warned the region could become critically short of water once seasonal food processing begins next week.
Chief engineer Peter Higgs says this significantly raises daily water requirements. "That could add another third to our need so instead of being 21,000 cubic metres we could be going up to 28,000 cubic metres of water we need, so that's why we are moving into a very critical situation."
Mr Higgs says water may have to be cut off to parts of the city for a number of hours.
Earlier, Richard Burke, the general manager of vegetable grower and processor LeaderBrand, said the industry would be able to find ways to conserve water.