I'm seconding everthing that has been said by T. here. It's definitely not conducive to receiving the most/best answers to your question, that is, using Slang. Correct me if I'm wrong, but I believe Monkey Water and Gunpowder are slang terms referencing different preparations of Black Tar Heroin prepared for use by a route of administration other than injection. Monkey Water being a solution of Heroin and Water and Gunpowder being an attempt at turning the Opium Latex into a dry powder than can be insufflated. For our purposes, this means we are talking about the same drug than.
There are no practical differences between the two. It's going to be largely based upon the effectiveness of your administration how potent the effects will be. Also, I believe your question is too general to get the answers you're looking for. We don't generally like the type of thread like "Heroin, tell me everything there is to know". It's not that we don't want to, but it's pretty time consuming stuff man. Could you maybe be a little bit more specific?