2006 Water Comprehensive Plan - City of Bellevue

The future build-out demand projections for each pressure zone are listed by operating area inTables 4-4a, 4-4b, and 4-4c. The City of Redmond and other wheeled/wholesale customerdemands are included.The projected maximum day demand increases approximately 22 percent from the 39.1 mgdrecorded in June 1987 to 47.5 mgd at build-out. Because Bellevue is currently surrounded byexisting jurisdictions on all sides, the only major factor that could increase the demands muchbeyond the projected 47.5 mgd would be a change in zoning and development in response toregional growth management requirements. Successful implementation of additionalconservation efforts would decrease the projected ultimate maximum day demand by reducingper capita demand.Conservation Adjustments to Demand ProjectionsAdjustments to demand projections were developed to account for the savings in waterconsumption expected to occur as a result of implementation of plumbing code revisions andspecific conservation programs.Bellevue’s demand forecast without additional conservation, as shown in Table 4-4a ,includes previous achieved conservation savings, but does not include future any futureconservation. Therefore, an adjusted demand forecast was developed to account for futureconservation savings expected to result from continued implementation of plumbing coderevisions and Bellevue’s specific conservation program detailed in Chapter 5, WaterConservation.Bellevue’s initial demand forecast was generated by combining demographic data and wateruse factors. The demographic data includes information such as population, the number ofhouseholds, the number of people per household, and the number of square feet ofcommercial space. Adjusting the demand forecast for conservation involves reducing thewater use factors to reflect continued conservation. The water use factors used in thedemand forecasts without and with conservation are as follows:WithoutWithConservation ConservationSingle Family (gallons per capita per day): 92 87Multifamily (gallons per capita per day): 80 74Commercial (gallons per 1,000 sq. ft. per day): 90 89While Bellevue is committed to conservation and expects to continue conservation programsinto the future, the 2011 water use factors were used again for the 2025 and 2040 demandforecast, rather than further reducing demand for three reasons. First, conservation oftenbecomes more difficult and expensive in the future as the easiest savings opportunities areexhausted. Second, this provides a slightly conservative demand forecast, which provides amargin of safety in terms of system operation. Third, the opportunity to reduce the water usefactors further will occur during preparation of the 2012 Comprehensive Water Plan, whenmore is known about realistic expectations for those latter years.4-9