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Evidence Base for Large-Scale Water Efficiency Phase II Second Report (2010)

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In this report Waterwise examines the effectiveness of water efficiency retrofitting programmes in schools in three English regions and Scotland. Its aim was to demonstrate the benefits, from both the water company and schools perspective, and to inform future water company activity. It draws on data from about 600 schools, four water companies and five water company school retrofitting programmes. The study suggests achievable water savings between 0.58 and 1.78 m3/pupil/year, as well as significant carbon emissions and energy savings. Costs amounted to £0.41 to £0.72 litre/day, which compares to the cost of water savings achievable through domestic retrofits.


I am delighted to introduce this final report of Phase II of the Evidence Base project. The Evidence Base represents the best current available knowledge of water efficiency in the UK. It has made a significant contribution to the development of water efficiency by gathering robust evidence from water company retrofitting projects and using innovative analysis methods to guide water company retrofitting activities in both homes and in schools. The original Evidence Base report – in October 2008 – for which I also Chaired the Steering Group, was widely acknowledged to have been extremely useful in plugging the information gaps, and was used by both water companies and Ofwat during the 2009 Price Review in England and Wales

However, the first report posed almost as many questions as it answered, which is why the Ministerial Water Saving Group agreed that it should be kept updated. As a result Phase II was specifically designed to best assist the water industry, regulators and policymakers in supporting the development of water demand management options as resource options – including in the context of carbon targets.

This report provides a single reference point for all that has been learned from Phase II of the Evidence Base. It summarises the outputs from the February 2010 and December 2010 reports. The report makes the case for large scale water efficiency in homes and schools, including through the first evidence on longevity of water savings.

This report will help companies start to build the case for their future water efficiency retrofitting projects in both price reviews and water resources management plan processes. The recommendations included in this report suggest ways in which water companies, manufacturers and retailers can help to make water efficiency a more viable option. Waterwise will release a separate paper setting out recommendations for water efficiency policy and regulation drawing specifically on this report. There are a number of areas where more work is required as the project moves into Phase III, but the results in this report should give water efficiency practitioners confidence that they can deliver water savings cost-effectively through retrofitting projects in both homes and in schools.

The Evidence Base Steering Group has approved a strategy for the development of the Evidence Base as the project moves into Phase III. In addition to continuing to improve the evidence base in domestic and schools retrofitting, this will further develop the evidence in areas including small and medium-sized enterprises, new build and grey/rain water recycling for non-domestic customers and metering, smart metering and tariff trials (when combined with retrofitting). One of the main aims of the Evidence Base will also be to help water companies and wider stakeholders to gain a greater understanding of how customer engagement, including where combined with retrofitting, can helpto change customers’ water-using behaviour. The aim is to integrate feedback from customers into analysis of water efficiency projects to achieve this.


This final report of Phase II of the Evidence Base Project includes new data on the effectiveness of domestic and schools projects in addition to summarising what has been learnt from the two previous reports: on domestic water efficiency retrofitting (the February 2010 report)1; and water efficiency retrofitting in schools2 (the December 2010 report).

Under further work in the February 2010 Phase II report, the following was described:

“Probably the biggest area of uncertainty in the cost-benefit analysis for water efficiency is how water savings are sustained over time. Further research is required that seeks to understand how well, over the medium- to long-term, water savings are sustained.”

The reason for revisiting four of the nine trials originally analysed in the February 2010 report was toimprove the industry’s understanding of the extent that water savings from domestic water efficiency retrofitting trials are sustained (longevity of water savings). The trials for which further information is included are:

Severn Trent Water’s Water Efficiency Trial
Sutton and East Surrey Water’s Preston Water EfficiencyUnited Utilities’ Home Audit Study
Yorkshire Water’s Water Efficiency Trial

On the schools side data is presented from two new water efficiency retrofitting projects which will help to reinforce the data included in the December 2010 report. The following projects are included in this report:

The Environment Agency’s Schools Water Efficiency Grants Project Essex & Suffolk Water’s Schools Water Efficiency Programme.