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.
The Smell of Molten Projects in the Morning 
My hat’s off to you. I don’t often get outgeeked on fire/life safety issues.
It’s a nasty job, but somebody’s gotta do it … [grin]
Or in other countries, take the pressure difference between floors and divide by 10 — and there’s your storey height in metres, near enough. Divide by your preferred value of g instead if you want to be all fancy and accurate like.
Heck, even we USA-ians can divide by ten!
Now, if only we’d make the change and be done with it, life would be so much easier. [heavy sigh]