A Tap-Left-On and Slow-Leak Witness for an Elder Living Alone: A Single-Point Water-Flow Design with a Computed Detection Budget

Design and computed detection budget for a whole-house water-flow witness for an elder living alone, sensing flow at a single meter point with no per-room plumbing. SIMULATED, NOT MEASURED; nothing was built, installed or tested in an occupied home. A rule of 30 minutes continuous flow by day, 15 minutes at night, and 2 minutes at or above 18 L/min detects a basin tap left on at 4 L/min in 30.0 minutes by day (120.0 L lost, 108.0 L reaching flooring) and a burst pipe at 25 L/min in 2.0 minutes (50.0 L), at a simulated false-alarm rate of 0.0005 per month over 2,000 simulated months of the stated legitimate pattern. The structural blind spot is printed at full size: the smallest continuous leak the design can ever catch is 0.40 L/min, and a 0.15 L/min underfloor leak delivers 216 L per day, reaching 500 L in 2.31 days and 6,480 L in 30 days, undetected throughout.