Old concrete pipes in Milton's urban water supply could be leaking 490,000 litres of water a day, at a cost of nearly $50,000 a year.
At the Clutha District Council's district assets committee meeting on Thursday, council staff said between 2001 and February this year, a total of 130 leaks were detected in the concrete pipelines.
Council senior water services engineer Ani Satterthwaite said pipe joint failures caused leaks and, if not fixed, resulted in more water that needed to be treated to meet the same supply demand.
Potentially the cost of the estimated volume of water loss of 490,000 litres was in the order of $48,000 per year, she said. Undetected leaks would also undermine the stability of surrounding ground and roads.
Councillor Joanna Lowrey said it was ''critical'' to get the work done.
''Water is a high commodity and I don't think we should have leaks.''
Council district assets manager Jules Witt said staff were proposing to replace only the broken concrete pipes, not all the pipes.
Ms Satterthwaite said 38 leaks were found by water loss management contractor Detection Services in February - more than the number of repairs in any year in the previous 12-year period.
However, she said this could be due to the fact that without the use of detection equipment, leaks might go undetected until the adverse consequences became visible on the ground.
Between 2001 and 2012 there was no significant increase in demand in Milton, other than the supply to the Otago Corrections Facility in 2007. The daily average flow production of the new Milton water treatment plant had increased from 1400cu m per day when it was commissioned in 2008 to 2000cu m per day in 2012.
Ms Satterthwaite said the increase of the plant's flow production could be due to water losses caused by leaks in the reticulation. Staff were now monitoring the plant's flow production and night-flow trending to confirm this theory.
A flow-meter on the distribution pipeline at the reservoir is scheduled to be installed by the end of June to help assess flow production at the water treatment plant.
Milton's water supply features about 28km of pipelines made up of a variety of materials - including concrete, cast iron, polyethylene, PVC and asbestos cement.
The council expected 1km of concrete pipelines would need to be fixed over the next year and planned to install four flow-meters in strategic locations in the reticulation network to monitor the water loss in the system. The estimated cost of this is $175,000.
Council staff are expected to make a submission to the draft annual plan requesting the council consider revising the Milton water supply renewals budget by bringing forward the $146,700 budgeted for pipeline renewal in the 2014-15 year.
Pipeline renewal budgets are loan-funded and impact on rates. However, council staff said savings might be made by combining the work into a larger contract.
