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SFPUC Wholesale Customer Water Demand Projections ... - BAWSCA

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SECTIONFOUR<br />

<strong>Water</strong> <strong>Demand</strong> Forecasting<br />

Agency Population Projection Source Selection<br />

The DSS population projections were tabulated in 5-year increments and graphed for each<br />

wholesale customer. Each of these population projections was then applied in the DSS model to<br />

create preliminary water demand projections with and without plumbing codes, which were also<br />

tabulated, graphed, and submitted to the wholesale customers.<br />

Each wholesale customer was asked to select one of the population projection sources based on<br />

the unique characteristics of their service area and consistency with local land use plans and<br />

policies. The exception to this is Stanford University. Residential account growth for Stanford<br />

University was projected using increase in dwelling units rather than population projections.<br />

Table 4-1 summarizes each wholesale customer’s population projection source selection, 2001<br />

base-year population, and corresponding 2030 population derived using the methodology<br />

outlined above.<br />

4.2.2 Use of Employment <strong>Projections</strong><br />

As described above, the DSS model uses growth in number of accounts and end uses to estimate<br />

future water demands. For each wholesale customer, the 2001 estimated service area<br />

employment (total jobs in service area) was directly related to the number of 2001 commercial<br />

and industrial accounts. Growth in those accounts was estimated using an employment growth<br />

rate or, in two cases, a total population growth rate. Table 4-1 summarizes 2001 DSS<br />

employment and 2030 employment projections for each wholesale customer based on the growth<br />

rate from their selected projection source for commercial and industrial accounts. An<br />

employment projection was not developed for Los Trancos County <strong>Water</strong> District (LTCWD) or<br />

Stanford University. LTCWD includes only residential accounts. Stanford University used other<br />

parameters such as increase in building square footage to forecast growth in Non-Residential<br />

accounts.<br />

ABAG was the only published source of employment projections available for the <strong>SFPUC</strong><br />

wholesale customers. For each wholesale customer, yearly service area employment growth rates<br />

were developed for the years 2001 to 2030 using the methodology described in Section 4.2.1<br />

above. ABAG service area blends, summarized in Table 3-4, were used to create the service area<br />

specific employment growth rates and projections.<br />

4.3 PLUMBING CODES AND NATURAL REPLACEMENT RATES<br />

In the forecasting process of the DSS model, fixture models incorporate the effects of natural<br />

replacement and plumbing codes to adjust the end-use water usage over time using a yearly<br />

average of fixture conditions for accounts with applicable end uses, including base-year existing<br />

accounts and new accounts. Natural replacement of a fixture occurs due to failure, aging, or<br />

remodeling. Plumbing codes require that new and replacement fixtures meet specified standards<br />

of efficiency. Table 3-9 lists the historical and current plumbing codes.<br />

4-4

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