SFPUC Wholesale Customer Water Demand Projections ... - BAWSCA

SECTIONFOUR
Water Demand Forecasting
continue to isolate potable accounts that would be switching to recycled water over time. The
following wholesale customers provided information on approved and funded recycled water
programs which was included in base year and/or future demand projections:
• City of Milpitas
• City of Palo Alto
• City of Redwood City
• City of Santa Clara
• City of Sunnyvale
Appendix D provides a complete summary of recycled water information provided by the
SFPUC wholesale customers.
The customer-billing data obtained from each customer were solely for potable water
consumption. If recycled water information was provided by a wholesale customer, a new
account category for recycled water was added to their DSS model. Recycled water use was
assumed to be 100 percent outdoor (irrigation) use.
4.5 SUMMARY OF WATER DEMAND FORECASTING
The water demand forecasting process detailed in this section consists of the following basic
steps:
• Projecting growth in the number of accounts
• Applying the fixture models to accounts with applicable end uses, using yearly estimated
replacement rates and plumbing codes to arrive at end use percentages for each account
• Adding up the water usage per end use in each billing category to get total new consumption
per account per year
• Multiplying the per-account usage by the number of accounts
• Adding UFW as a fixed percentage per year
• Adding recycled water use on top of the potable demand to arrive at a total demand curve,
where applicable
For each year in the forecast, the number of accounts for each billing category is increased from
the prior year by the corresponding years growth rate. This growth rate is based on either a
population or employment projection. Each account has an associated water use, in gallons per
day, determined by the model calibration and affected over time by applicable fixture models. So
adding a new account adds the applicable water use, which is then summed to make a new total
consumption for each year. UFW is then added as a fixed percentage and that sum is the
projected water production for that year. So year by year the projection is extended to the ending
year (30 years from the start). The next section provides the 2030 demand projections resulting
from the water demand forecasting.
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