national multiple family submetering and allocation billing program ...

easonable assumption since there is no reason why the type of billing system being used would
affect the likelihood of a survey being returned.
Because water billing data were available for all of the respondents it was possible to
compare water use patterns for the respondents. It should be kept in mind, however, that the
water use statistics derived from the postcard survey respondents are inconclusive by themselves
because they are uncorrected for other property characteristics that might influence water use. It
is important to keep in mind that there may be other factors (age of property, size, rent, etc.)
which impact water use that are not factored into these analyses of the data from the properties
owned or managed by postcard survey respondents. The purpose of the multivariate modeling
effort (presented later in this chapter) was to correct for these factors. Only an analysis that takes
these factors into consideration can be considered more conclusive about the cause of water use
savings. However, it is instructive and suggestive to look at water use and to evaluate
differences using the postcard survey respondents, especially since it is the largest available
sample.
The 2001 and 2002 annual water use per unit summary statistics for the properties
reported on by the postcard survey respondents are shown in Table 5.5. Overall, submetered
properties used between 7.4 and 9.2 kgal less water per unit per year on average than the in-rent
properties. RUBS properties used between 1.0 kgal less and 1.5 kgal more water per unit per
year on average than in-rent properties. Hot water hybrid properties used between 2.1 and 3.4
kgal more water per unit per year on average than in-rent properties.
In both 2001 and 2002 the median RUBS water use was slightly higher than the median
in-rent use while the median submetered water use was lower than the in-rent use value. The
median annual water use per unit is lower than the mean (average) value within each billing
method, suggesting a heavy tailed (possibly skewed as well) distribution. The lognormal
distribution is often taken as a good fit for residential water use if the population is
homogeneous. In this case, this is not so. There is no particular reason to expect that effects are
multiplicative rather than additive. Consequently, the analysis was done on the natural scale.
However, as a check, the analysis was also ran on the log scale, and found no qualitative
difference in the conclusions.
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