The boss of Wellington Water is defending asking the public to think carefully about water usage, despite thousands of leaks being identified across the region.
There's a one-in-four chance the region will enter level four water restrictions this summer, meaning all outdoor water use would be banned and indoor use would be cut by half.
Wellington Water chief executive Tonia Haskell said the region had thousands of water leaks and she estimated 45 percent of the region's water was being lost.
"There's a lot of water that is just disappearing out of our network."
She added: "Fixing leaks and renewing the pipes is top of the list for most of our councils," as they prepared their long-term plans.
Limited funding and resources mean it won't be a quick fix, and everyone has to conserve water where they can.
It was hard to ask residents to limit their water use when they could see a leak outside their property, she said.
"But we just need to understand that every bit helps and we're doing as much as we can to fix the leaks and if everybody can help with their water use then between us we've got a good chance of getting water all summer."
The El Niño summer has been modelled and there was a 24 percent chance that demand would get too close to "the headroom of supply" so usage would need to be reduced "across the board" to ensure everyone could be supplied with safe drinking water.
Haskell said residents were starting to tune into the impact of a long hot dry summer on the region's water supply.
She appealed to them to consider water use and report any water leaks.
"We're still trying to get the big leaks fixed first because they produce the most water loss but having all of the leaks on our record and keeping an eye on them is something the public can really help us with."
She said the region had a finite amount of water and under current conditions which had produced rain and not a lot of hot weather it had "enough headroom" to supply enough water for people's needs.
"And also I think our conservation measures are hitting home and people are starting to value their water."
However, as summer temperatures kicked in, more water would be used and the supply from rivers and the aquifer would decrease so "the buffer" between supply and demand would be put under strain.