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

Council Water Supply team looking for water leaksChristchurch 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 approximately 200 sub-zones.

Water loss work before the earthquakes

Before the 2010 and 2011 earthquakes around 20 zones in the city and around 2-3 water supplies on Banks Peninsula were tested each year, usually carried out in the winter months to avoid interference with high (irrigation) water demand, and involved:

  • 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.

The city-wide average result prior to the earthquakes was 165 litres per connection per day.

Post-earthquake water loss work

The 2010 and 2011 earthquakes had a significant effect on Christchurch’s water supply network. Leakage and therefore the amount of water extracted and the cost to pump it throughout the city increased markedly. The Stronger Christchurch Infrastructure Rebuild Team (SCIRT) was tasked to return Christchurch’s non-revenue water to the pre-earthquake level (165 l/conn/day).

The 18-month SCIRT programme involved carrying out nightflow tests and leak detection work in all urban Christchurch and Lyttelton Harbour Basin (Lyttelton, Governors Bay and Diamond Harbour) water supply areas.

The final citywide average MNF rate (including Lyttelton, Governors Bay & Diamond Harbour) was 133.5 l/conn/day.

The testing of all zones within the 18-month period was only made possible by introduction of seasonal irrigation offset calculations which allowed year round testing.

Conclusions and looking ahead

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.

Since June 2015 Council is focusing on getting all Banks Peninsula water supplies tested as they were not part of the SCIRT programme. In the long term work will commence again in the city as water loss reduction work is a continuous effort.