It is likely that a broken pipe caused or significantly added to a slip which took out utilities in the Lower Hutt suburb of Point Howard, Lower Hutt Mayor Campbell Barry says.
Residents, some who were forced out of their homes by the landslide, said they had been warning the council about the leaking pipe for months.
Hutt City Council said whether residents will be able to get their vehicles past the slip site should be decided this afternoon.
The council said it was working to restore water and road access.
The slip ruptured a gas line and cut power for a time - and 165 homes were still without water on Wednesday morning.
Parts of Nikau and Howard Road remain closed.
Wellington Water said its crews were assessing what repair work was needed and expected to be able to restore water to the most affected residents once it had site access.
The wastewater system has not been affected, so water collected from the tankers stationed in the area could be used to refill toilet cisterns, Wellington Water said.
Residents who needed to collect their pets could use walking routes to collect them.
Barry, who is also chairperson of Wellington Water, said they were working through "who knew what when" but their current focus was on the response to the slip and restoring the water.
"It appears likely the broken pipe has caused or at the very least significantly contributed to the slip."
Council would be looking in to Wellington Water's processes for prioritising leaky pipe fixes and has asked for a range of information, he said.
"When were complaints lodged, what were the actions taken, what were the assessments made from those who were on site initially and we'll be getting that information over the coming days and we'll be able to report that back."
All the information would be released once it was available, he said.
There was an issue with water leaks across the entire region and it was a matter of prioritisation, he said.
"Not just the amount of water that is potentially coming from a leak but the topography of the land and any risk to services or issues like slips and that's something we'll be looking into further around Wellington Water's processes to get that reassurance that those things are factored in to actually prioritising the jobs."
A temporary solution for restoring water was being worked on and it was hoped it would be restored by 8pm on Wednesday, Barry said.
"There are currently water tanks in place and pedestrian access on the road but currently vehicles are still unable to get through."
Hutt City Council was advising Point Howard residents to boil their water until further notice and said there are two water tanks and 12 portaloos in place.
'You could see...it would undermine the bank' - resident
Point Howard resident Heather Armishaw was fuming after the landslip saying she reported a leaking pipe to Wellington Water several times but nothing was done.
Wellington Water declined an interview on Morning Report saying to check their social media for updates.
Armishaw told Morning Report they first noticed the issue when water began to flow down a stormwater channel at the bottom of their property just before Christmas.
They traced it to where it was coming out just below the road down a steep bank, she said.
"The flow increased steadily over January and February and the last time we measured it, it was about 130 litres a minute which is an Olympic sized swimming pool in 11 to 12 days."
Hutt City Council passed the complaint onto Wellington Water which visited the area several times, Armishaw said.
Eleven days ago they discovered that some of the bank below the road had slipped, and her neighbour warned the council if something was not done, it would undermine the road and cut services, she said.
"At this stage one of our neighbours, who is a retired civil engineer, he called the council and advised them if something wasn't done very soon more of the bank would slip and the road could be undermined with the loss of services - and that's exactly what happened on Monday night."
The slip was not weather related, she said.
"We've been watching the water coming out of this bank and you could see that it if there was much more of it it would undermine the bank and that's exactly what happened."
RNZ
