Being a sucker for infrastructure and numbers, the fire sprinkler system pressure gauges in the motel stairwell proved irresistible.
The first floor gauge shows a nice round 100 psi:
Up on the second floor, it’s 90 psi:
With a different brand of gauge, it’s also 90 psi on the third floor:
Maybe 85 psi on the fourth:
Squinting at the parallax, call it 80 psi on the fifth:
At the top of the vertical pipe on the fifth, on the other side of a valve, we return to the original valve company at 78 psi:
Water weighs just over 62 lb/ft³ at room temperature, which works out to 0.43 lb/in² per vertical foot. Not having packed my laser distance widget, I’ll guesstimate 12 feet and 5 psi per floor.
A quick graph with an eyeballometric straight-line fit:
Call it 0.42 psi/ft, which is pretty close to the right answer.