5.1 WE Prerequisites
Key Takeaways
- WE has three prerequisites — Outdoor Water Use Reduction, Indoor Water Use Reduction, and Building-Level Water Metering — all required for any LEED BD+C certification level.
- Indoor Water Use Reduction requires a 20% reduction below the calculated baseline derived from EPAct 1992 fixture flow rates (1.6 gpf water closets, 1.0 gpf urinals, 2.5 gpm showers, 2.2 gpm private lavatories, 0.5 gpm public lavatories, 2.2 gpm kitchen sinks).
- Outdoor Water Use Reduction is met by either using no potable water and no other natural surface or subsurface water resources for landscape irrigation, or by reducing landscape water demand by at least 30% using the EPA WaterSense Water Budget Tool.
- WaterSense-labeled fixtures and fittings must be installed for all applications where a WaterSense label exists, with manufacturer documentation kept for the certification submittal.
- Building-Level Water Metering requires permanent meters that record total potable water and any sub-system that uses more than 10% of total building water, with monthly and annual data shared with USGBC for five years post-occupancy.
Why the WE Prerequisites Matter
The Water Efficiency (WE) category in LEED v4 BD+C carries 11 possible points, but the gateway is the three prerequisites — they are required, score zero points, and a project that fails any one of them cannot be certified at any level. Expect 8-12 exam questions across all of WE, and at least two of them will probe whether you can distinguish a prerequisite (mandatory baseline) from a credit (optional point opportunity).
The prerequisites are rooted in two federal references that you must know cold:
- Energy Policy Act of 1992 (EPAct 1992) — sets maximum flow and flush rates for plumbing fixtures sold in the United States. LEED uses EPAct 1992 rates as the baseline against which reductions are measured.
- EPA WaterSense program — a voluntary partnership that labels fixtures and fittings using at least 20% less water than the federal baseline while meeting performance criteria.
Prerequisite 1: Outdoor Water Use Reduction
Intent: reduce outdoor water consumption.
A project meets this prerequisite through one of two compliance paths:
| Option | Requirement |
|---|---|
| Option 1 — No Irrigation Required | Show that the landscape does not require a permanent irrigation system beyond a maximum two-year establishment period. Native and adapted plants, hardscape, and natural precipitation must carry the site. |
| Option 2 — Reduced Irrigation | Reduce the project's landscape water requirement (LWR) by at least 30% from the calculated baseline using the EPA WaterSense Water Budget Tool. |
The WaterSense Water Budget Tool factors in:
- Local evapotranspiration (ETo) rate
- Plant species factor (low, medium, or high water-use plants)
- Density factor and microclimate factor
- Irrigation efficiency (drip ~0.85-0.90; spray ~0.625-0.70)
- Effective rainfall
Design moves that earn the prerequisite include xeriscaping with native and adapted species, removing turf grass, switching from spray to drip irrigation, and adding smart irrigation controllers (rain sensors, soil moisture sensors, ET-based controllers).
Prerequisite 2: Indoor Water Use Reduction
Intent: reduce indoor water consumption.
Projects must reduce aggregate indoor potable water use for plumbing fixtures and fittings by at least 20% below the calculated EPAct 1992 baseline.
EPAct 1992 Baseline vs. WaterSense Targets
| Fixture | EPAct 1992 Baseline | Typical WaterSense Level |
|---|---|---|
| Water closet (toilet) | 1.6 gpf | 1.28 gpf |
| Urinal | 1.0 gpf | 0.5 gpf or less |
| Public lavatory faucet | 0.5 gpm | 0.5 gpm (already at baseline) |
| Private lavatory faucet | 2.2 gpm | 1.5 gpm |
| Kitchen sink faucet | 2.2 gpm | 1.8 gpm |
| Showerhead | 2.5 gpm at 80 psi | 2.0 gpm |
(gpf = gallons per flush, gpm = gallons per minute)
Required, not optional: every newly installed fixture and fitting that has a WaterSense-labeled equivalent in its category must be WaterSense-labeled. The project team submits manufacturer cut sheets confirming flow rates and WaterSense certification.
Calculating the 20% Reduction
The reduction is fixture-weighted, not a simple flow-rate average. You calculate:
- Baseline annual gallons = sum of (baseline flow × duration × daily uses × full-time-equivalent (FTE) occupants and visitors × 365).
- Design annual gallons = sum of (design flow × duration × daily uses × FTE × 365).
- % reduction = 1 − (design ÷ baseline).
Default usage assumptions come from the LEED reference guide (e.g., 5 toilet uses/day for female FTE, 1 for male FTE plus 2 urinal uses, 0.2 kitchen-sink uses at 15 seconds, etc.).
Prerequisite 3: Building-Level Water Metering
Intent: support water management and identify opportunities for additional water savings.
The project must install permanent water meters that measure:
- Total potable water use for the entire building and associated grounds, and
- Each separate water use that exceeds 10% of total building water consumption (for example: irrigation, cooling tower makeup, process water, reclaimed water).
Projects must commit to sharing monthly and annual whole-project water use data with USGBC for five years after occupancy (or until the building changes ownership). The five-year commitment ends if the project transfers ownership or lessee, but the meters themselves are a permanent fixture.
Quick Memory Hooks
- 3 prerequisites, 0 points — required to certify.
- 20% indoor, 30% outdoor (or no irrigation), 5-year data share.
- EPAct 1992 = baseline; WaterSense = better.
- WaterSense labeling is mandatory wherever available, not optional.
A LEED BD+C project team installs ultra-low-flow water closets and certifies a 22% reduction below the EPAct 1992 baseline. However, the design team uses a non-WaterSense-labeled showerhead with the same 2.0 gpm flow rate as a WaterSense model because the architect prefers the finish. Has the project satisfied the Indoor Water Use Reduction prerequisite?
Which scenario satisfies the WE Prerequisite: Outdoor Water Use Reduction?