During the power outage from "Fay" , I was wondering why the plumbing would still work ?

Question

what math was guiding this phenomena? Commode still flushing and refilling, water still running out of taps (cold of course)..........

Answer 1

Either the water treatment plant where you get your water still had power (Most by regulation have a back-up power source (generator))

or

Your pressure tank on your well still had pressure.

Answer 2

Your pumping station may be in an area that still has power, or it may be operating on backup power.  Your mains may be supplied from a gravity-fed storage tank or reservoir.

Answer 3

all of that is mechanical and uses no electricity