Water Efficiency
Indoor water dominates
Water Efficiency in ID+C is almost entirely indoor water use. The prerequisite requires a 20% reduction from a calculated baseline, and the credit rewards progressively deeper reductions in tiers. The baseline uses EPAct 1992 fixture flow rates: water closets 1.6 gallons per flush, urinals 1.0 gpf, lavatory faucets 2.2 gpm at 60 psi, showerheads 2.5 gpm at 80 psi, and metering faucets roughly 0.25 gallons per cycle. Occupancy comes from the design documents, distinguishing regular occupants from transient users.
Other water credits
Where the project has cooling towers or process water, cooling tower water use (cycles of concentration, blowdown, treatment) and permanent water metering may be in play. If the tenant genuinely controls landscaping, outdoor water use reduction applies; most interior fit-outs do not.
Traps
- Building the baseline from the design fixture rather than the EPAct rates; the baseline is fixed by code-era assumptions.
- Letting a lower assumed occupant count inflate the reduction percentage; baseline occupancy is held constant.
- Forgetting process loads such as ice machines, dishwashers, and cooling towers when the credit references total indoor water.
- Claiming outdoor or irrigation credit on a project with no tenant-controlled landscape.
Rule of thumb
Percentage reduction equals baseline annual gallons minus design annual gallons, divided by baseline annual gallons. Change one variable at a time and keep occupancy fixed, or the calculation is not defensible.