Several hundred households in Nelson can use the water supply again, now an accidental chlorine overdose has been flushed from the system.
The city council warned residents in the suburb of Atawhai just before 2pm on Thursday to avoid drinking from taps or having showers.
A malfunction in a dispenser put more than 10 times the usual amount of chlorine into the supply.
The council's manager of utilities, Howard Schuppan, says the system was flushed out by about 4.30.
However, he says there may still be highly chlorinated water in some of the smaller supply pipes leading to individual properties.
He says residents who notice a strong chlorine smell or taste in the water should run their tap for a few minutes; if it does not change within five minutes, they should call the council.
