What is water loss reduction?
Water loss reduction is the name of the programme that assesses the amount of water that is not appropriately used (non-revenue water - NRW) in the city’s reticulation system.
The main objective of water loss work is to reduce the amount of NRW - the quantity of water extracted from our water supply wells, minus the quantity of water used and delivered to our (metered) residential and commercial customers.
NRW has two components and, while every water supply system is different, often both components contribute equally to NRW through:
- Physical losses due to leakage from pipes (both on private property and on the reticulation system)
- Administrative losses due to un-metered consumption (water for fire fighting, fire sprinkler testing, water taken during construction of sewers/subdivisions, water used by street cleaners) or illegal connections and under-registration of water meters.
Physical losses are dependent on 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 which would measure flow rates at night (when water consumption is the lowest). Advice was sought from an international leakage expert and experience shared with water suppliers worldwide.
For the purpose of measuring minimum night flows and NRW, Christchurch’s reticulation network can be temporarily isolated into many sub-zones.
At present around 20 zones are tested each year, usually carried out in the winter months to avoid interference with high (irrigation) water demand, and involves:
- Testing of water mains and submains to identify water leaks (both on the Council network and on private property).
- Repairing water leaks on Council assets by Council maintenance contractors.
- Notifying property owners if a leak was identified on private property.
- Night flow testing to establish the minimum flow in each zone. Businesses that are known to consume large volumes of water at night are monitored using data loggers.
- Calculation of NRW - the amount of non-revenue water and real losses.
In 2006, Christchurch City Council started water loss work on Banks Peninsula.
Akaroa and Takamatua were undertaken first and in 2007 Birdlings Flat, Little River and Duvauchelle were leak surveyed and flow tested for the first time.
In 2008 Akaroa, Takamatua, Lyttelton, Governors Bay, Diamond Harbour and Wainui were tested.
In addition to the 20 zones in the city that get chosen each year and the work on Banks Peninsula, 10 zones in the city are tested annually using permanent test sites that were specifically designed and installed for straight forward monitoring. These 10 zones are called District Metering Areas (DMA).
The tests in those 10 DMA zones are done annually to establish whether a clear trend in terms of NRW can be identified.
Results
Christchurch
The annual NRW results appear to follow a cyclic pattern of decreasing and increasing values. The 2005 result was the lowest so far, but has gradually increased again to 148 litres per water connection per day. This is still below Council’s target of 150 litres per water connection per day. This target has been established as a balance between environmental benefits and the cost of undertaking the work.
Key successes for Christchurch City in 2008 were:
- 238 leaks on Council infrastructure were identified and repaired.
- 367 leaks on private properties were identified; owners were notified and large leaks were followed up with Council site visits.
- The amount of water saved through repairing the leaks equals approximately 1.47 per cent of the total annual water extraction. The actual saving might be lower as it cannot be verified that all leaks on private property have been repaired.
- The volume of water saved would result in approximately $46,000 operational savings (if all private leaks were repaired).
Banks Peninsula
Akaroa and Takamatua were leak-surveyed and flow-tested for the third time. Whilst Takamatua’s NRW has reduced compared to 2007 it is still relatively high for such a small water supply. Akaroa’s NRW result remained almost the same and is well below 150 litres per water connection per day.
Lyttelton, Governors Bay, Diamond Harbour and Wainui were leak surveyed and flow tested for the first time. All night flow tests resulted in very high values of NRW in those zones.
Key successes on Banks Peninsula in 2008 were:
- 52 leaks on CCC infrastructure were identified and repaired.
- 61 leaks on private properties were identified; owners were notified and large leaks were followed up with Council site visits.
- The amount of water saved through repairing the leaks equals approximately 9.25 per cent of the total annual water extraction. The actual saving might be lower as it cannot be verified that all leaks on private property have been repaired.
- The volume of water saved would result in approximately $75,000 operational savings (if all private leaks were repaired).
It is expected that continued leak detection work and investigative work (such as identification of illegal connections, cross-connections) in the Banks Peninsula water supply areas will further reduce NRW.
Conclusions
Christchurch's water is world class 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.
Over the past years we have tested Christchurch's entire reticulation system. Overall, our reticulation system seems to compare very well to other places around New Zealand and internationally, however this programme needs to be ongoing in order to keep us in this position as ageing pipe work can dramatically increase the level of NRW over the years.
