PROCESO: SIE-GPG-OOPP-045-12 La Máxima Autoridad del Gobierno

2.7.1 Household Water Demand Studies

International and UK studies have examined the effects of various possible influencing factors to residential water demand. Apart from the price of water, the factors most commonly explored in the literature are household demographics and weather related ones, while age is one of the least examined variables. Household income, occupancy, property size and precipitation are some of the most frequently used determinants in water demand models and their effect on domestic consumption has been well

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The effect of price of water was not examined in the present study for various reasons. First, it has been shown that water demand is fairly price inelastic and most UK households are currently billed a flat yearly rate which covers the domestic supply and quality maintenance costs and which does not vary enough from one household to another. Only a minority of customers are being charged based on their actual consumption. However, as UK water suppliers have recently started applying universal metering schemes and with increasing numbers of households becoming metered in the near future, the present research could prove to be of little use if it incorporated price as a factor of influence.

Although information on household income and property size were not available for this research, they were incorporated in the analysis using a proxy variable, ACORN class (see Methodology Chapter).

Many studies have used OLS regression methods to model water demand, not accounting for the effects that the co-existence of time variant and time invariant elements might have on water consumption. This study addresses this limitation by developing multilevel (mixed) models of water demand. Additionally, this study uses per capita consumption (PCC) as a unit of measurement and not aggregate census tract or total household consumption as many studies have utilized, providing more detailed information about demand on the customer level.

Finally, it is important to note that in their recent report, CIWEM (2016) stress that there is still a relatively poor understanding of how and why demand varies from property to property and they recommend that projects focusing on water using behaviours are developed.

2.7.2 Residential Water Efficiency Studies

Domestic water demand management, especially leakage detection and adoption of water conserving devices, has started gaining momentum both in the UK and globally. However, when it comes to the evaluation of programmes that incorporate devices installation and distribution, a robust methodological framework is non-existent. It is

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clear that a proper evaluation framework should incorporate important contextual factors and that it should be built based on them. As thoroughly described in this chapter, Australia and the US are leading the domestic water efficiency research for the past 20 years. Detailed guidelines for water efficiency programmes evaluation are only found currently through Integrated Resource Planning (IRP) framework, a comprehensive decision-making process developed in Australia and which is considered as best practice for water companies internationally. However, the methods that are proposed by IRP cannot be fully adopted by companies with data limitations. This problem is due to the fact that the evaluation process outlined throughout the framework mainly uses data intensive methods such as participant-control group comparisons and micro-component analysis that monitors the effect of each water saving product on different end-uses. Advanced micro-component techniques, which are considered as best practice by water efficiency experts worldwide, are rarely used in European residential water conservation studies. Although micro-component analysis was not possible in the context of this research, an evaluation of water savings was realized using mixed modelling techniques and by making full use of all available data provided by the two water companies. Most UK studies in this field use consumption means comparison methods to explore possible changes in water demand as a result of water efficiency measures. Some of them do not include control groups in their analysis, not accounting for external factors that may heavily influence consumption trends. It is highly recommended that control groups are used in water efficiency evaluation studies for comparison purposes.

It is observed that a large proportion of water efficiency research measures water savings on the household level and very often water savings are calculated for a uniform average number of occupants. However, the usefulness and robustness of this approximation is doubtful as it does not account for between households heterogeneity and it does not add to the precision required in water efficiency evaluation. Therefore, the present study uses PCC (per capita consumption) as the preferred output variable in the formation of the multilevel models of water demand.

As already discussed, technological changes such as retrofit programmes and other non- price policies have gained less attention than price-policies, mainly because of the lack of

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adequate data (Millock & Nauges, 2010). In parallel, the effect of educational programmes and awareness campaigns has proved to be significant mainly in times of water scarcity and crisis and it usually diminishes within a year (AWE, 2010).

Literature review points out that there is still much to explore and discover regarding the effectiveness of installing water saving devices and fittings, especially in areas where research on this matter is in its infancy such as in the UK. In the UK context, research and analysis of water savings lack the skills and the methods’ precision that some Australian and American studies demonstrate.

Detailed information on local residential consumption is essential for the appropriate implementation of such programmes and for achieving greater water savings. Specifically, water companies usually do not investigate the effect that their pilot retrofitting programmes had in households of different characteristics although this information would provide useful insights on the local population’s water use. Also, such data would be invaluable for future water efficiency initiatives as they would set the right direction for effective implementation on suitable population samples, thus potentially enabling bigger water savings through water-saving technology.

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