Water Efficiency
Inside, outside, and metered
Water Efficiency has three prerequisites in BD+C: Outdoor Water Use Reduction (roughly 30% below baseline, or no potable irrigation), Indoor Water Use Reduction (about 20% below baseline), and Building-Level Water Metering. Credits then stack on top with deeper reductions, cooling tower water use, and advanced metering.
Baselines are fixed, not historical. Indoor baselines come from the fixture flow and flush rates in the 1992 Energy Policy Act, with WaterSense as the efficient benchmark: toilets 1.6 gallons per flush baseline versus 1.28 for WaterSense, lavatory faucets 2.2 gallons per minute versus 1.5, showerheads 2.5 versus 2.0, urinals 1.0 gallon per flush versus 0.5 or waterless. Outdoor baselines derive from peak evapotranspiration for the planting palette.
Cooling tower credits reward higher cycles of concentration, which cut make-up water and blowdown. Alternative sources - rainwater, graywater, reclaimed water - can be substituted, and substituting them often converts a marginal credit into a strong one.
Traps
- Confusing the 20% indoor prerequisite with the 30% outdoor prerequisite.
- Percentages are always relative to the calculated baseline, never to last year's bills.
- Process water (kitchens, laboratories, cooling) is treated separately from fixtures and is easy to forget.
- Metering must be permanent and building-level; a temporary construction meter earns nothing.
Rule of thumb
Toilets dominate indoor savings; irrigation dominates outdoor savings. Worked example: a project installing 1.28 gpf toilets, 1.5 gpm faucets, and 2.0 gpm showerheads has a strong start on the indoor prerequisite but no credit until a calculation against the baseline is submitted.