South West Water Explicata WET Report 1 (2007)

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This report by South West Water analyses a water efficiency trial for households. The study comprised ‘Control’ and ‘Sample’ households, 109 and 430 respectively, which were offered a variety of water-saving devices for installation. The analyses prior and after device installation indicate percentage water use reductions of approximately 10% per household, which declined to 6% after seven months following the installation. The water- saving device percentage reduction was greater the larger the number of devices installed in the household.

Executive Summary

1 The WET project involved measuring the effectiveness and costs of fitting a range of self selected water efficiency devices to measured customers’ houses.  These devices were chosen from a range made available by the Company.

2 The project consisted of the following key stages:

  • Choosing locations and sample sizes
  • Recruiting participants and setting up database
  • Choosing the devices to be installed
  • Selecting and training plumbers
  • Installing devices
  • Taking readings
  • Analysing readings

3 The trial was set up to measure the effect of a group of customer selected water efficiency devices and not to measure the effectiveness of any individual device.  Therefore number of customers who selected just one (and the same) device is too small to from which to draw statistically valid conclusions.

4 The analyses indicate initial water savings of approximately 5% per household, reducing to 4% six-to-seven months after device installation.  

5 Similar savings were found across different Council Tax bands but differing savings were found across property types.

6 It is suggested that savings might be greater from unmeasured customers on the basis that measured customers are likely to have already embraced an element of water saving behaviour.

7 The report shows that the Long Run Marginal Cost of this Water Efficiency Trial is 496 p/m3

8 The Appendices to this report contain a lot of information (letters, questionnaires, information sheets etc) which it is hoped will be useful to anyone setting up a similar trial.