Quick question from a green plumber: in a 12-unit retrofit last spring, dual-flush 1.1/1.6 gpf averaged 1.24 gpf, while 1.0 gpf pressure-assist averaged 1.06 — so which really wins once you factor leak risk and how people flush? Anyone else track numbers like this?
Did you reprogram the dual-flush canisters to 0.9/1.28? In a 16-unit last spring, that dropped our dual-flush average from your ‘1.24 gpf’ to about 1.15 with no uptick in leak calls, while pressure-assist still edged it on raw gallons…
In a 24‑unit last fall, the biggest drop came from swapping in adjustable fill valves (Korky 528MP) and setting the bowl‑refill dial to the bowl spec — cut overfill about 0.08 gpf on both two‑button and pressure‑tank installs. > pressure-assist still edged it on raw gallons… Same for us until the refill tweak plus a ‘tap don’t press’ lid sticker; the short‑flush share jumped and the averages tied within about 0.02. WaterSense has a quick note on refill ratios: WaterSense Product Search - Toilets | US EPA — have you checked your refill vs bowl volume?
On my retrofits, the spread comes from ‘silent leaks,’ not the label: quarterly dye checks and preemptive seal swaps at 18–24 months keep two‑button setups around 1.15–1.20, while 1.0 pressure tanks hold about 1.05 but spark more noise/hammer calls. What’s your water hardness and service cadence? That leak‑first maintenance pattern has saved more water for me than chasing small gpf deltas — those sips add up faster than my coffee.
Pure gallons favors pressure-assist — your 1.06 beats 1.24 — but behavior was the lever for me: we flipped the split-button so a quick tap defaults to the light flush and added a tiny ‘tap = light’ sticker, cutting average about 0.08 gpf with no leak uptick. @walter41 is right that leaks skew it; if you tracked light vs full selection in that 12‑apartment retrofit last spring, the usage mix probably explains most of the gap.