Tendencias de Emisiones

It is common in water demand research that researchers explore the influence of household specific factors on water consumption. Often referred to as ‘demographic variables’, various household attributes and characteristics are used in regression models as predictors of per capita consumption since the 1960s. The household appears to be the most appropriate unit to explore the relationship between a population and domestic demand (De Sherbin et al., 2007) while the number of household specific factors used in each study is dependent on data availability and on the size of the households’ samples. In some instances, although there are available data on many different household factors, sample sizes are too small to incorporate all of them; otherwise there is the risk of over specification or overfitting of the water demand models. Thus, demographic variables should always be used with caution and according to previous relevant research findings. In this study, there were several different demographic variables tested for their effect on per capita consumption. However, as anticipated, some proved to be stronger predictors than others and they were chosen for inclusion in the multilevel analysis for the two case studies. These variables were ACORN class, the number of residents, the number of water saving devices fitted and the dummy variable for the water efficiency programme which indicated the programme take up period for each property.

178 6.3.1 The Effect of ACORN Class

The ACORN classification system can be used in a range of planning studies, including water demand management ones. Per capita consumption in ACORN class 1 properties was 7.1% higher than in class 5 ones (p<0.05) in the first case study (Anglian Water Services). In the second case study (Essex & Suffolk Water), the difference between ACORN class 1 and 5 in terms of PCC was 3% (p<0.05). Although the ACORN class coefficient for the second case study was smaller, the effect of the variable was highly significant, indicating that more affluent residents consume more water than the financially stretched ones. The most likely explanation for this is that richer homes usually contain more water amenities, both indoors and outdoors and that due to their affluence, they might be less concerned about their water bills. This finding is also supported by relevant research which shows that suburban affluent homes use more water than the rest household types (Russac et al., 1991; Kowalski and Marshallsay, 2005; Harlan et al., 2009). It can be inferred that ACORN class can be used as a proxy variable for income and social status.

As Domene et al. (2006) point out, the effect of income and social status is more prevalent in the households that have gardens and therefore when outdoor water use exists. However, often researchers critique the use of population classification systems such as ACORN categorization as for their representativeness (Clarke et al., 1997; Maksimovic et al., 2003).

The effect of ACORN class was also explored in terms of the water savings that each category achieved due to the water efficiency programmes in which the households participated. As seen in section 5.6.1, the interaction between the efficiency programme variable and the ACORN class dummy variable was negative and highly significant. This result illustrates that the programme was more effective in reducing PCC in the ACORN class 5 properties rather than class 1 properties, an effect which also appeared in the means comparison analysis in section 5.4.1. In simpler words, it supports the notion that the more financially stretched households reduced their consumption to a greater extent because of the efficiency programme while the most affluent ones showed the least water savings. After conducting further multilevel analysis for the participating households in

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the H2eco project (2nd case study), clustered by ACORN groups (section 5.6.2) it was

shown that ACORN class 1&2 properties decreased their per capita consumption by 11.8% (p<0.001) while classes 4&5 presented an impressive 19.7% decrease (p<0.001) on average. These results agree with Australian research (Turner et al., 2005a) which showed that the indoor water saving potential in low income homes is 18% greater than in other income groups. Lawson (2015) in his study on the H2eco efficiency programme

concluded in the same results, pointing out that ‘Urban Adversity’ homes achieved the biggest water savings. The study by Lawson (2015) was the only study found in the literature which examines the influence of ACORN class on a water efficiency programme’s effectiveness in the UK.

As seen in Section 5.6.2, the two models for different ACORN classes produced exactly the same coefficient for the household size variable (9.8%, p<0.001). This result demonstrates that ACORN class has no effect on the relationship between PCC and household size, showing that in households of more than one residents PCC will be lower than in properties of a single resident, regardless of ACORN class.

6.3.2 The Effect of the Number of Occupants (Household Size)

The number of occupants is a very commonly used variable in water demand studies and it usually appears to be significantly associated with total water use and per capita consumption. Many researchers (Al-Noaimi, 2004; Gaudin, 2006; Foster, 2011) suggest that per capita consumption decreases with an increase in household size (i.e. number of residents). Most studies indicate that there are some economies of scale with many residents in a house, where food preparation, dish washing, gardening and other activities take place despite of the household size and are capitalized on a shared living environment (Hoglund, 1999; Arbues, 2000; Polebitski and Palmer, 2010; Foster, 2011). Moreover, as far as water conserving habits are concerned, research by Gilg and Barr (2006) showed that households of fewer residents are more likely to be committed environmentalists, therefore it is more probable that they will achieve larger water savings.

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water reduction achieved through the water efficiency programmes were thoroughly tested in the present study. In the context of the first case study, it was shown that people living alone consume 7.6% (p<0.05) more water per day than those who live in a five- member home.

An interesting finding was the significant negative coefficient for the interaction between sunshine hours and the number of occupants. This finding illustrates that during periods of sunny weather, a person would consume much more water than usual if he/she lived alone than if he/she lived together with more people. A possible explanation for this is summer outdoor use. Water quantity used for irrigation is larger during sunny weather, due to evapotranspiration and decreased frequency of rain events and as explained earlier, garden watering is going to take place regardless of how many people live in a particular household. As already discussed earlier in Section 6.2, past research (Balling, 2008; House-Peters et al., 2010; Bao, 2013) suggests that there is a relationship between a household’s consumption sensitivity to weather and socioeconomic characteristics, although this relationship appears to be weak in most instances.

For the second case study, a 8.7% difference in PCC (p<0.001) was observed between single person households and 5-people households, with people living alone consuming a larger quantity of water on average. A 10% temperature increase would result into a 1.3% increase in the consumption of single occupancy homes (p<0.1), while there was no significant effect in the case of households of 3 or more members. A 10% increase in days with rain of more than 1mm could lead to a 0.6% decrease (p<0.05) in consumption for households of 3 members or more, while there was no significant result for single occupancy homes, as shown in the multilevel model (clustered by household size-Section 5.6.3). The models also suggest that a person who lives with two or more people in an ACORN class 1 household consumes 2.7% (p<0.1) more water than an average ACORN class 5 household resident who lives with two or more people. In the case of people who live alone, there was no significant difference in PCC among different ACORN classes. It is common for ACORN class 1 residents to be prosperous pensioners who stay at home during the day. As such, it is inevitable that they consume more water than other residents of other ACORN classes who are usually working away from home during

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weekdays. The same results were produced in previous studies by Lyman (1992) and Fox et al. (2009). Unfortunately, information on the age of the occupants was not available in this study.

It was also shown that the interaction term of the water efficiency programme and the number of residents was positive and significant (p<0.001), indicating that in households with more occupants, the water efficiency programme was less effective, as the PCC decrease that was caused by the devices installation became smaller. This results agrees with the previous study by Gilg and Barr (2006). Specifically, the multilevel model showed that after the programme launch there was a 20.2% (p<0.001) decrease in consumption for one person households and a 10.8% (p<0.001) decrease for households of three or more residents.

6.3.3 The Effect of the Number of Fitted Water Saving Devices

Multilevel models for the second case study showed that the more water conserving devices were installed in a household the more effective the water efficiency programme would be in decreasing consumption, a result not surprising at all. In the disaggregated by ACORN class models, this effect was more prevalent in ACORN class 4&5 households and this can be attributed to the fact that class 4&5 homes are usually smaller and with less water using appliances than the larger homes that belong to ACORN class 1 and that may need several more efficiency retrofits for their water savings to be substantial.

In the analysis that was conducted for separate groups of household sizes in Section 5.6.3, it was shown again that the more water conserving devices were installed in a household the more effective the water efficiency programme would be in decreasing consumption. This effect appeared to be stronger for one person households and due to the economies of scale effects explained earlier in this Section, this effect becomes weaker in homes of two or more residents.

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