The project has a subterranean parking garage for 49 vehicles (19,247 sqft) that is within a mile of the Napa River. With this close proximity to the river and a high water table, the parking garage has ground water infiltration that is being pumped out at 1000 gallons per day. The captured ground water is being filtered (e.g. motor oil, fuels, paints/stains and solvents, asphalt products, concrete, herbicides, pesticides, and TSS, etc.) and pumped out of the garage to the city storm drain system, according to city code and San Francisco Bay Area Storm Water Management Agency Standards. The question is, could this captured ground water be used in the building as graywater for flushing toilets and urinals to offset potable water use and thereby qualify for LEED NC v2.2 Water Efficiency credits?
The applicant is proposing to use groundwater that has been pumped to prevent flooding to reduce potable water demand by using it for flushing toilets and urinals for WEc2. This strategy is acceptable as long as the water is only being pumped to keep the building dry; sinking a well or pumping more water than is necessary are not acceptable strategies. If the water that the project team is using is water that would be produced and discharged anyway, then the project team may use include the reused water in the calculations for the credit. The water quality of the water being used in toilets and urinals should be addressed in cases of recycled water that is untreated or minimally treated. States and regulatory agencies tend to require the water to be up to potable water standards before it goes into the toilet or sink. Note that the water quality should meet local standards and consult manufacturer recommendations for compatibility of parts with greywater use. As a point of clarification, captured groundwater is different than greywater; the term should be changed to alternate on site water sources in this CIR. Applicable Internationally.