Council's water loss and leakage reduction programme assesses the amount of non-revenue water (NRW) in the network.
Non-revenue water is the quantity of water extracted from our water supply wells minus the quantity of water used and delivered to our metered customers.
Non-revenue water has two components, and while every water supply system is different, often both components contribute equally to non-revenue water through:
Physical losses are dependent on the age and condition of the water supply network and the water supply pressure. Administrative losses are dependent on how much effort is made in repairing water meters and identifying illegal connections.
Christchurch City Council has been carrying out water loss reduction work since 1996.
A lot of initial work was done to establish techniques for surveying the losses in the system and to design and construct structures that would measure flow rates at night (when water consumption is the lowest). The advice was sought from an international leakage expert and experience shared with water suppliers worldwide.
For the purpose of measuring minimum night flows and non-revenue water, Christchurch’s reticulation network can be temporarily isolated into approximately 200 sub-zones by closing valves so that there is only one single feed into a zone at which point the night flow is measured. The zones range in size between 40 to over 2,000 water connections/properties.
Council surveys approximately 40 zones per year using night flow testing and then carries out leak detection work and a second night flow test in 20 of the 40 zones. It takes approximately 5 years to survey the entire city.
The methodology is as follows:
The above steps can take several weeks to complete for a single water loss zone if there are many leaks in a zone.
Christchurch's water is precious and therefore we want to continue utilising this resource in a sustainable manner. Water loss due to leakage is also costly because of electricity and the pumps that are used to distribute the water in the network are expensive.
Overall, Christchurch's reticulation system seems to compare well to other places around New Zealand, however, this programme needs to be ongoing in order to keep us in this position as ageing pipework can dramatically increase the level of non-revenue water over the years.
In the long term Council will investigate creating permanent district metering areas as water loss reduction work is a continuous effort.