Warren,
When pressure testing, fill completely with water and then pressure up. In
case of catastrophic failure the burst will be harmless, and the pressure
can be instantly relieved since there exists no actual air volume. All
hydrostatic tests are done in this method.
You need only test for a working pressure of 30 to 50 pounds per square
inch. Potable water is supposed to be kept at 42 psi which is the pressure
that most considered harmful bacteria are not likely to survive. Of course
in the city of Houston if they kept the pressure they are supposed to, most
of the shoddy water mains would fail so most are at a pressure of 35 psi if
your lucky. We do however have four domed stadiums and a fifth we absolutely
need instead of things like water main replacement from 100 years ago. Hope
this helps you.
-Eddie-
Houston, TX