Plumbing air pressure test?

Most use a regulator.  They are inexpensive and easily put in line to the water inlet.  I don't know that they are needed in most campgrounds but they don't hurt.

Great point brought forward JandL differentiating between hydraulic and air pressure.  I have just finished blowing out irrigation lines on 3 golf courses over the last 3 days and while we maintain 120 - 125 lbs of water pressure in the lines during the summer using the 375 CFM air compressor we may get up to 36 - 38 lbs air pressure in those same lines while blowing out/purging water out of the lines.  When water is purged and air comes out of the sprinkler heads, the sound is something like a jet ready for take-off.  This is especially true at the end when we open a 2" line to let the air out quickly so we can disconnect the hose, this takes about 12-15 minutes.  When the air comes out you better have on some really good ear protection otherwise you will end of going deaf or ruining your hearing, the sound of the air escaping is deafening.