This CIR describes our methodology for developing baseline water use for PSU Broadway Housing, a residential project. Please advise if this methodology is acceptable. Our baseline water use estimates have been calibrated to data from a 1999 American Water Works Association (AWWA) study on residential end uses of water. The study lists per capita daily water usage rates for conventional and "more efficient" water fixtures. The conventional fixture values were used for all baseline fixtures, except toilets. For toilets, the water efficient fixture rate was chosen as it corresponds to 1.6 gallons/flush, the current code standard. The AWWA information can be accessed on the following website: http://www.awwa.org/Advocacy/pressroom/statswp5.cfm All fixtures used code or standard flow rates; the daily uses and/or durations were adjusted for calibration, such that the overall gallons/person/day for each fixture type matched the study values. Calibration of Baseline Water Use by Fixture Fixture Type -- AWWA LEED Baseline Kitchen sink -- 6.7 = 2560 gal/day/384 occ. Lavatories -- 4.4 = 1680 gal/day/384 occ. Faucets -- 11.1* Sum of above = 11.1** Toilet -- 9.6* 9.6 = 3686 gal/day/348 occ. Shower -- 12.6 12.5 = 4800 gal/day/384 occ. Clothes Washer -- 15.1 15.0 =5760 gal/day/384 occ. * Based on low-flow fixture rates (1.6 gal/flush) ** The AWWA study listed only the overall faucet usage; breakdown to usage by kitchen sink and lavatory was based on professional judgment.
The LEED Reference Guide and the LEED calculators (found in v2.0 Calculator or v2.1 Letter Template) provide guidance on the calculation methodology that should be used for this credit. A list of all water-using fixtures and frequency-of-use data needs to be input into the spreadsheet. Frequency-of-use data includes the number of male and female daily uses, the duration of use and the water volume per use. The water use calculations are based on building occupants\' usage of fixtures that are necessary for the occupancy of the building, such as for drinking water and conveying sewage, and does not include process loads (e.g. dishwashers, clothes washers). For LEED calculations, the baseline case uses fixtures that meet the Energy Policy Act requirements (see page 100 of the LEED v2.1 Reference Guide for EPAct fixture ratings). The design case would then account for water efficient fixtures that meet or exceed the Energy Policy Act requirements. Calculations also include water-source strategies such as rainwater and graywater use. The 1999 American Water Works Association (AWWA) study on residential end uses of water does not provide information on whether the baseline calculations are based on fixtures that meet the Energy Policy Act of 1992, and should therefore not be used for LEED calculations. As there are no set criteria for determining daily use or duration of use, the project can estimate both of these items based on the project and occupants or refer to this study as a guide in determining the frequency-of-use data.