The Water Regulations (or rather WRAS, the advisory scheme) have a
recommended procedure for pressure testing of supplies. ISTR though
that although some sort of pressure testing is mandatory in commercial
environments, it isn't on domestic installations.

Building Regulations mandate pressure testing of sewers, but not water
supply IIRC.

However pressure testing is widely used by professional plumbers, and
particularly for UFH.

A suitable gauge for dry air testing with a 15mm push fit on it is now
about 30 quid (http://www.screwfix.com/prods/72940/...ools/Plumbing-
Tools/Pressure-Test-Equipment/Monument-Dry-Pressure-Test-Kit).

I use one along with a car tyre footpump. It's not foolproof. I just
had to tackle an inaccessible joint with a very slow drip on it, that
didn't show under air testing. (My one and only poor solder joint in a
thermal store installation). But it will show most problems.

Possibly the much higher pressure, professional test kits will show
even the slightest leaks up.

(As an aside, when I used to work on ultra-high vacuum systems years
ago, mass-spectrometer gas analysers had just become available. You
connected up your vacuum system to the gas analyser, then went round
squirting helium gas at each joint, until the analyser showed up that
the gas had found a way inside the vacuum system - I don't think
plumbers have these *yet*)