In the meantime, Wellington Water is installing 15 flow meters, known as small area monitors, throughout the region to better understand where non-visible leaks are occurring.
Three of these were installed in Upper Hutt in August.
Two of the three areas regularly recorded periods of zero flow during the night, but one had a minimum flow of 17 litres per minute.
That's the equivalent of about 25,000 litres a day.
Wellington Water suspects most of that is likely to be leakage because overnight usage is generally low.
The leak has been found in an area that encapsulates 61 properties, where Wellington Water has since visually identified one leak from a private property.
The owner has been issued with a repair notice and once the work is done, Wellington Water will refer back to the night flow data to see whether there are any further leaks.
Water usage in Upper Hutt has skyrocketed recently from an average of about 375 litres per person per day in 2019 to almost 420 litres in 2020.
Wellington Water has attributed this to a period of high leakage earlier this year.
Across the region, usage is generally trending up as is minimum night flow information, which suggests an increasing number of leaks.
The supply-demand balance for water in Wellington was last assessed in 2017, but a Sustainable Water Supply Target and Policy report shows the situation has changed.
The population growth rate has exceeded those earlier forecasts, meaning the region will need to find a new water source well before 2040.
It could be needed as early as 2026 if demand and projected population growth continue on the trajectory they're on now.
An initial 10 per cent reduction in demand would be required over the next six years in the capital to offset growth over the same time period.
That's the same as a reduction of 40 litres per person per day in gross demand.
Alternatively, a new source and associated network capacity increases would cost more than $250 million.
A move to universal water metering could reduce residential water demand by up to 20 per cent.
But not so much by influencing consumer behaviour as through identifying leaks in supply pipes and fittings, the report said.
The business case for such a move, due to be made public before the end of this month, is being prepared for Hutt, Porirua, Upper Hutt and Wellington city councils.
South Wairarapa and Kāpiti Coast councils already have them.
Kāpiti Coast District Council introduced metering in 2014 and within 18 months peak day consumption decreased by about 26 per cent.
In that same time period, 443 leaks were found and 97 per cent of them were fixed.
