Oxycodone is water soluble, yes. However it has a very high oral bioavailability - you really don't gain much from shooting it, just a load more risk. If you are going to IV a pill then you really need to get yourself a micron filter (see here) otherwise you are injecting talc and all sorts of other nasty filler/binders into your bloodstream, which can lead to lung disease. Also make sure you don't heat it - oxycodone is soluble in cold water, heating it just causes extra nasty stuff from the pill to dissolve too.