I have been "waterlining" black tar for years, and I can only say good things about it. It's socially acceptable, I just have an allergy medicine bottle that I can use anywhere. Definitely less wasteful than smoking.
as far as the question about the brown powder that turns to tar, they get a big hard chunk of black tar and stick it in the food processor/blender whatever. This gives them a brown powder that when slightly heated, turns back to tar. In my experience, the harder and more translucent dope is, the more potent it is. I know other junkies that say the gooey, soft, black stuff is better, but I think that's BS
basically the mexicans are too lazy to take the last few steps to turn tar into number 4 heroin, so we end up with an "acetylated opium" product.
This really doesn't say much about potency though, I have had black tar in denver and portland that was waaay better than the white powder I got in New Jersey.