sorry for my other "crack". i was having fun with the water thing. lol. on a more serious note Bob is 100% correct.most of the regular members know to only use hpa, nitrogen, or helium, but keep in mind there are lots of noobs that find their way here and take in the info. i regularly see or am asked about using oxygen. which is also a big NO NO. also regardless of the gas these are very high pressures we are talking about and could be fatal if dealt with foolishly. ONLY use HPA (high pressure air), nitrogen, or helium in your pcp's. anything else may be your last mistake.