I wouldn't bother trying to separate the impurities. I doubt there's that many or that they're going to interfere with the trip, especially when used rectally. It doesn't really matter if the water is distilled or tap if it's going in your ass. It's a dirty place; all the bacteriostatic whozits and whatzits in the world aren't going to change that.
So I'm guessing Rizla is to rolling papers what Kleenex is to snot rags? Why them versus TP or a tissue - or heaven forbid, an empty capsule? Whatever you want to do, I just think it's funny how much I see posted about people "bombing" happy powders in brand name paper intended to be burned.