Two hundred homes are without water in the Dunedin suburb of Opoho after high winds brought down trees.
The winds are part of a storm system that has also buffeted Christchurch and Wellington.
A Dunedin City council spokesperson, Rodney Bryant, says roots from one tree brought down by the wind have ruptured a water main.
He says it's too dangerous to carry out repair work and residents will be without water until midday on Wednesday. Tankers are delivering water to affected households.
Dunedin police said earlier they'd been inundated with calls about trees and power lines coming down. One fallen power pole triggered a fire in a pine plantation near Brighton.
In Christchurch, the Fire Service says it has been flat out responding to calls about falling trees and small fires.
In Wellington, wind gusts of up to 140 kilometres an hour brought down trees and trolleybus wires.
Brief respite likely on Christmas Day
Despite the wind, some parts of the South Island sweltered, with Dunedin, Kaikoura and Timaru recording temperatures in the 30s.
The rain and high winds were expected to ease on Tuesday evening, though more rain is forecast for Fiordland and Westland on Wednesday.
MetService says strong northerly winds behind the front will push temperatures up in eastern parts of the South Island.
It says the unsettled weather is likely to continue throughout the week as a series of fronts crosses the country.
Forecaster Andy Downs says there will be a brief respite on Christmas Day before another front arrives later in the weekend.