New Zealand ILI’s

ILIs in New Zealand in 2014/15

New Zealand was one of the first countries to adopt The IWA Best Practice Water Balance and Performance Indicators in 2002, The original 2002 version of the Benchloss software and User Manual was updated in February 2008, supplemented by the simpler free CheckCalcs software, and Water Loss Guidelines were published early in 2010. The delivery of drinking water, storm water and wastewater is managed by Councils and a small number of Council Owned or Controlled Organisations.

The Water New Zealand National Performance Review is the pre-eminent annual review of the performance of these services. 41 Councils and council controlled organisations covering over 85% of New Zealand’s population of 4.6 million participated in the 2014-2015 review; participation rates improved by 25% over the previous year’s survey. Ranges of system size, other infrastructure and pressure parameters, are shown in the Table below.

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Two thirds of the 41 participants issued water restrictions in 2014/15 which suggests there is pressure on the availability of water supplies. However, international comparisons of per capita residential consumption, leakage and customer metering suggest there is much room for improvement. While most non-residential properties are metered at the property line/edge of street, such metering is are not yet common place for residential properties; only 7 participants had full residential metering. So perhaps unsurprisingly, NPR participants had the highest average per capita residential water consumption (275 litres/person/day) of the international benchmarks for Australia, Europe, Netherlands, Pacific Region and the UK. This lack of metering makes the assessment of real losses problematical in most Utilities,

24 participants have undertaken leakage management efficiency assessments using the Infrastructure Leakage Index (ILI)/. After adding data from 5 Utilities with 83% to 99% residential metering to the data from the 7 fully metered utilities, then excluding several data sets where there was a lack of data to calculate ILI, or some other apparent data inconsistency, a set of 6 ILIs were calculated for 6 Utilities. These are, in ascending order, 1.4 to 5.8 for:

Tauranga CC, Christchurch CC, Kapiti DC, Whangerei DC, Kaipara DC and Hauraki DC.

These are shown in the bar chart below, with ILIs and average pressures classified from  ‘Very Low’ to ‘Very High’ in accordance with the Leakage Performance Categories used in the 2015 EU Reference Document

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Calculated ILIs for several fully metered distribution systems in the greater Auckland distribution systems, were in the range 1.0 to 1.5 around 2010, but none of these are calculated in the 2014-15 National Performance Report. ILIs calculated for systems with few metered residential services ranged from 1.8 to 13.5 (median are not included in the above bar chart as they are subject to greater uncertainty,.

It is clear that Water NZ is seeking to systematically improve their leakage performance and leakage performance assessment procedures, and several constructive comments are offered in this respect.

  1. Given the difficulty of assessing Real Losses from a Water Balance in systems with unmetered residential properties and high summer peak demands from garden irrigation and tourism, water balances or Snapshot ILI (Section 5 of the Water New Zealand, Water Loss Guidelines (2010) referenced below) from minimum night flows outside the higher seasonal demand periods, are useful supplementary approaches.
  2. Page 56 of the NPR states that ‘ILI does not account for system pressure, which is a strong determinant of waterloss. Water loss comparisons should be made between systems of similar operating pressures’ , but that is not correct. It would be better stated in next year’s NPR as ‘ILI allows for current system pressure in the UARL formula. However, pressure is a strong determinant of leak flow rates and burst frequency. The current system pressure is not necessarily optimal, and excess operating pressure and pressure transients are not beneficial; they should be reduced wherever feasible, without breaching minimum standards of service for pressure’.
  3. The Department of Internal Affairs requires calculation of real losses as a percentage of system input volume, as non-financial performance measure PM2. This contradicts IWA recommended good practice, as it is a zero-sum calculation which is strongly influenced by changes in consumption. Demand restrictions in 2014-15, and longer term reduction of excess residential consumption by metering, will cause unnecessary and avoidable confusion if PM2 is used to compare performance or track changes in leakage management performance, see KPIs fit for purpose.

References

Water New Zealand, 2016: National Performance Review 2014-15       April 2016

Water New Zealand, 2010: Water Loss Guidelines, prepared for Water NZ by A.Lambert (ILMSS Ltd/Wide Bay Water) and R. Taylor (Waitakere City Council)

Comments on this ILI data by ILMSS Ltd do not purport to represent the opinions or policies of any individuals or organisations which assisted in provision of the data.

Future Updates: Countries which already have sufficient good quality ILI data to justify a separate Webpage within Global ILIs are invited to Contact ILMSS Ltd.

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Webpage dated 6th May 2016