Toilet Flush Volume
Average flush volume across all toilets in the home.
Spec by tier
This requirement steps in stringency by tier. Each tier inherits and tightens the value.
Scope
Every toilet installed in the dwelling unit, including dual-flush models. Bathtubs, urinals (residential only), and bidets are excluded.
Requirements
Performance targets
- 01.
Identify the rated GPF (gallons per flush) for every toilet in the home. For dual-flush toilets, use the higher of the two flush volumes (full flush) for compliance calculations.
- 02.
Calculate the average rated GPF; the average must meet the tier threshold in the "Spec by tier" table.
- 03.
Alternative pathway: submit a Home Water Score report meeting the tier threshold.
- 04.
New construction at Silver and above must install only toilets meeting the tier threshold — averaging in older fixtures is not permitted on new builds.
Documentation
Evidence the inspector / Institute will need.
- 01.
Photo of each toilet's manufacturer rating (cast or printed on the bowl behind the seat or on the underside of the tank lid) showing GPF.
- 02.
OR completed measurement record (bucket-and-stopwatch method) for each toilet.
- 03.
OR Home Water Score report.
Guidance
How dual-flush counts
For a 1.6/1.1 GPF dual-flush toilet, GreenStar counts the 1.6 GPF full flush — not a weighted average. The rationale is that occupants do not always select the appropriate flush, so the standard assumes worst-case usage. Single-flush 1.28 GPF WaterSense toilets typically outperform dual-flush models on this basis.
Retrofit options
For existing toilets above the threshold: (a) replace the toilet with a WaterSense unit, (b) install an adjustable dual-flush conversion kit (some are accepted by GHI; verify with the inspector before relying on this), or (c) install a tank fill-cycle diverter / displacement bag to reduce flush volume — last-resort, only useful for marginal cases.
Resources
- EPA WaterSense — Toilets →
Federal high-efficiency spec: 1.28 GPF max. Lists certified product database.
Example — Averaging a mixed home
A 3-toilet home has units rated 1.6, 1.28, and 1.28 GPF. The average is 1.387 GPF — passes Certified (<1.6) but fails Silver (<1.3). Swapping the 1.6 GPF unit for a 1.28 brings the average to 1.28 — passes Silver and Gold (≤1.0? No, 1.28 > 1.0).