Stormin Mormon wrote, on Tue, 01 Jul 2014 20:04:23 -0400:

I suspect the wharfs are gravity feed from the
tank, nearly zero PSIG. Compared to mains on
real hydrants. Still, it may some day be the
only water to be had.

Yes. They're all gravity fed. There's really no other way
because you can't depend on electricity in a fire anyway.

Mine is about 14 feet below the bottom of the tanks, so,
that's roughly about 1/2 an atmosphere, which is about
7 or 8 psi (which doesn't sound like much to me).

Luckily, the FD can *pump* that, but they told me at
the station they prefer the pool anyway, so, in "my"
case, they'd use the pool instead (which is more than
ten times larger anyway).