A critical leak in the capital's water pipes has been fixed after contractors worked through dismal weather today.

Photo: RNZ / Jacob McSweeny

The leak was found on Friday night and work was done through the night to put a temporary fix on it.

Wellington Water said the damage to the pipe, which was broken at the point where it connects to the main line, was likely to have been caused by the November earthquake.

The leaked water had eroded the sand underneath the road next to Wellington's central railway station and created a cavity about 4m wide and deep.

Wellington Water spokesperson Alex van Paassen said it took five hours to drain the pipe before welding could begin.

A team of ten contractors worked to fix the leak. Mr van Paassen said it would take a few more days to fix the hole that had been created.

Wellington Water general manager Gary O'Meara said the leak had taken a while to identify and a temporary repair had been put in place in the middle of the night on Friday.

If it had not been fixed by 6am yesterday, people would have had to start conserving water, he said.

Mr O'Meara said Wellington was vulnerable to future problems because the city was dependent on just one pipeline.

"There's a couple of key messages here," he said.

"We are vulnerable in an earthquake event. We kicked off a major project about 18 months ago with our client councils to actually look at the resilience of the networks and what we can do to increase that," he said.

He said one option was a second main cross-harbour pipe into Wellington.

"[It would cost] a large amount of expenditure to be able to do that.

"We are currently looking at options of a secondary main, cross-harbour or aquifer into Wellington to reduce the outage time that would happen in a major event," he said.

Wellingtonians needed to keep at least a week's supply of water in case of emergency.

"Wellington in a major event is likely to be without water for up to 100 days on the Eastern Suburbs currently.

"We're looking to peg that back with investment but for the first seven days after a major quake in Wellington there will be no supply of water in the worst case scenario.

"Residents are really required to be resilient for those first seven days."