Wellington's CBD, which could be disconnected from the water supply for up to 90 days after a major earthquake.

The heart of Wellington city, and the nation's government, could be cut off from the water network for three months if a major earthquake struck.

The fragile state of the city's water supply has been highlighted in a report by Wellington Water that reveals some suburbs would be disconnected for months.

It comes as the region's civil defence manager warns city residents to hoard more than the national recommendation for their personal stash.

JOHN NICHOLSON/ FAIRFAX NZ Suburbs furthest from the supply, such as Miramar, could take up 100 days to reconnect.

If there was a major quake, it would take about 100 days to reconnect all east Wellington properties to the network, and about 90 days for the CBD. That compares with 40 for Porirua, and between five and 30 for the Hutt Valley.

Wellington Water senior manager Mark Kinvig said the figures were the latest estimates, and now the organisation's five council owners needed to decide what level of service they wanted to provide, and how long they wanted to take getting there.

"If we carry on at our current level of investment, we will get there in about 50 years."

ROSS GIBLIN/ FAIRFAX NZ Wellington Region Emergency Management regional manager Bruce Pepperell said people should store enough water to last 10 days.

The presentation to the regional civil defence group said Wellington had three water supply plants, with its pipes crossing three faultlines.

Until water was reconnected to homes, people would have to face walking up to a kilometre to get their daily supply.

Porirua Mayor Nick Leggett, who is also the emergency management group chairman, said there hadn't been enough work done to upgrade water infrastructure.

"We've got to do things better, and we've got to do things faster."

He said that might mean taking money from "flashy" projects and redirecting it into infrastructure and resilience work.

Wellington Mayor Celia Wade-Brown said the reconnection times were a maximum needed to hook up every home in the affected areas.

She said planning was under way for a cross-harbour pipeline, and potentially for water extraction from an aquifer in Evans Bay, which could supply the eastern and southern suburbs.

There had been 1300 rainwater storage tanks sold in Wellington city and the council had been strengthening reservoirs and creating emergency supply tanks in communities, she said.

The likes of hospitals and the region's prisons would be priorities for reconnection.

Wellington Water spokesman Alex van Paassen said the organisation would discuss with its five council owners what they thought were the right levels of service for restoring supply, and what work was needed to achieve this.

"Obviously there are cost implications in levels of service; just as there are if there is no service."

Greater Wellington Regional Council chairman Chris Laidlaw said the cross-harbour pipe project could provide a valuable supply from Lower Hutt directly to Wellington city.

"It has the potential to make a major impact on a post-earthquake situation."

Wellington Region Emergency Management regional manager Bruce Pepperell said the national recommendation for home supply was three litres a person a day, for a minimum of three days.

But he said if a quake hit Wellington it would not be the same as in the likes of Christchurch.

"There are 30 different routes into Christchurch. We have two state highways, and they get broken if there's a little bit of water."

Emergency services would "move heaven and earth" to make water available in a convenient way for Wellingtonians, but three days would not be enough.

"It would not work as well as Christchurch, and therefore just accepting a generic statement that applies to the whole country – we would be underselling ourselves in the Wellington region."

Pepperell said his personal recommendation for Wellington would be to store enough water for 10 days.

WHY THE DIFFERENCE IN RECOVERY TIMES?

Wellington Water gets its water from the Hutt River, at Upper Hutt, the Waiwhetu aquifer extracted at Waterloo, and from rivers behind Wainuiomata.

That water has to be pumped to all of Upper Hutt, Lower Hutt, Porirua and Wellington.

Those long supply lines would be broken in places, so the areas furthest from the supply, such as Miramar and Karori, would take the longest to reconnect.

HOW MUCH, FOR HOW LONG?

The recommended minimum amount of water for home storage in the event of an earthquake is three litres a person a day, for at least three days.

Wellington Region Emergency Management regional manager Bruce Pepperell said he recommended 10 days for Wellington – and the 3 litres was for drinking only.

For a four-person family, this would be 12 litres a day for 10 days – the equivalent of 60 standard 2-litre fruit juice bottles.

If people also wanted to cook and wash, they needed to store closer to 20 litres.

For a family of four, this would be 800 litres for 10 days. That's three and a half bathtubs, at 225 litres each.

Hot-water cylinder water can be included as storage, but Pepperell warned that, in some cases, the water pressure from the supply was needed to get it out.

Water should be kept low down in a cool, dark place such as a cupboard, garage or shed. Bottles should be labelled with a date and replaced every 12 months.

STOCKING UP

Miramar resident Mark Simeon thought he was prepared for a big shake, but after hearing Kinvig's estimates he wasn't sure.

"I will be stocking up on those big 10-litre bottles now. I'll stuff them under the bed and in the roof. Especially now I am expecting a baby girl, I need to be prepared."

His current kit for himself and his partner included food, about eight litres of water and a first-aid kit, all of which was packed into his garden shed.

"I have got the basics and a bit more. Given those estimates, though, I am quite off the mark."