SFPUC Wholesale Customer Water Demand Projections ... - BAWSCA

SECTIONTHREE
Establishing Base - Year Conditions
Table 3-5
Dwelling Unit by Building Type from Census 2000
Assumed Number of Dwelling Units per
Building Type
Building/Complex
Single-Family
1-detached 1
1-attached 1
Multifamily
2-units 2.0
3-4 units 3.5
5 to 9 units 7.0
10-19 units 15
20 or more units 50
Mobile homes 50
Source: Census 2000 (U.S. Census Bureau 2002)
The number of dwelling units provided by the census was divided by the assumed number of
dwelling units per building to determine the estimated number of buildings (or housing
complexes).
Step 2: Apportioning Dwelling Units to Residential Billing Categories
The total number of “Single-Family 1-detached” buildings was compared with the number of
Single-Family Residential accounts in 2000 (obtained from billing records) to determine if the
“Single-Family 1-attached” buildings were represented by billing data. If not all the “Single-
Family 1-detached” buildings were represented in the Single-Family Residential accounts, then it
was assumed they were grouped with the Multi-Family Residential accounts. This grouping can
occur depending on how a wholesale customer categorizes townhouses, condos, etc. Some
agencies categorize these types of residences as multifamily while others may categorize them as
single-family.
The assumptions for number of dwelling units per building (or residential complex) were
adjusted to obtain a reasonable match between the number of buildings and the number of Multi-
Family Residential accounts in 2000 (billing records). The final number of multi-family dwelling
units was divided by the number of Multi-Family Residential accounts to obtain an average
number of dwelling units per account for each wholesale customer. Each value was assumed to
remain constant from 2000 to 2001 (base year).
Determining Average Household Sizes
Average household sizes are important parameters in developing an end-use model because they
provide a link between the customer-billing data (such as the number of Single-Family accounts)
and the end-use data (such as the residents use water in the accounts). Therefore, a complex
iterative process was used to ensure that the household sizes not only fit known demographic
data, but also produce reasonable water use results. The following steps describe the process
used in determining the average household sizes for single-family and multi-family residences:
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