Thousands of Hamilton residents are being told to ensure they have emergency water supplies to last a few days in case anything goes wrong in planned urgent, major repair work to a water main.
Part of the Waikato river bank collapsed a fortnight ago, damaging the Eastern Bulk Main that supplies water to around 27,000 homes.
It meant the Western Bulk Main and water stored in the reservoirs had to be relied on temporarily.
The city council has implemented alert level four, which meant no outdoor water use was permitted.
The council's city waters unit manager, she hoped the work that needed to be carried out would not cause problems for residents.
"However there are always unforeseen events, which may mean a planned or unexpected water outage may be required in terms of isolation of the two water mains," she said.
Ms Porter said the work was set to take several weeks and was likely to cost hundreds of thousands of dollars.