Most opioids will easily disolve in cold water, this is true.. fentanyl is a differn't story, but it's totally synthetic so it has differn't properties...
As for Dilaudid - I agree, any brand other then Knoll are just not ment for injection.. you can petition the lord with prayer but they just don't seem to cook up.. I have only actually tried with 2 other brands (Teva and Roxxane I believe) and both had CLEARLY been tweaked so as they turned the water to an un-usable slop .. it would be possible to do a cold water extract, but there isonly 4mg of drug in a pill (aside from the 8mg's which are almost NEVER seen) so it's not really worth it ..
So -
Generic Dilaudid - can't bang, might be able to cold-water..
Hydrocodone containing products - yes, you cabn cold-water these..
Oxycodone containing products - yup, cold water here we come.. this includes OxyContin, though I don't recomend you inject it..
Demerol - yes, you might need to use warm water first, then let it cool, but it will disolve..
Oxymorphone - I am sure it is soulable in water, though the only time I got any was in the injectable forum, in fact, there isn't an oral (tablet) form of this on the market, so you either get the solution to inject or you getthe anal-bullet which I have no idea if you could prepare it, I have never played with one..