I work for a plumbing company, and we recently put up some copper water pipes (~30mm) in a newly constructed building. The buidling isn't finished, and since it's below 0 degrees we can't test the pipes with water. So, we though about doing it with air instead. Some people tell me that this should never be done because it's simply dangerous, while others think it's fine. One question is how much pressure should be used, and for how long? With water we would test it for a couple of hours with 7-8 bars. Pressure during use is about 5 bars. Someone told me that air would perhaps leak out since air molecules are supposedly smaller than those of water. If so, how much (and how fast) should I allow to leak out before believing it to be some kind of bad joint somewhere...?