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 due to leakage from pipes both on private property and on the reticulation system. Leakage can be further broken down into:
- unavoidable leakage - very small leaks that are unable to be detected with equipment
- actual leakage - leaks that can be identified and repaired
- Administrative losses due to:
- unmetered consumption, such as water for fire fighting, fire sprinkler testing, water taken during construction of sewers/subdivisions or water used by street cleaners
- illegal connections and under-registration of water meters
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.
What the Council is doing
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 contractor isolates a water loss zone and performs a flow test to measure the water usage at a time when water consumption is considered to be lowest (i.e. at night, preferably winter). Known commercial high water consumers are monitored during the test.
-
If the night flow test result is high compared to previous tests then the contractor carries out a leak detection survey. This usually involves deploying acoustic loggers on valves and hydrants which indicate the general area of a leak, followed up with a walkover ground microphone survey to pinpoint the actual leak location.
-
Leaks on Council pipes are repaired, significant leaks on private property are reported to the property owner.
-
After all leaks on Council owned pipes have been repaired the contractor carries out a second-night flow test to confirm the night flow has reduced.
-
The night flow result and the number of water connections in each water loss zone are then used for calculating the overall leakage.
The above steps can take several weeks to complete for a single water loss zone if there are many leaks in a zone.
Conclusions and looking ahead
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.