Bong Water Flavours are one of those things you go to when you're a little bored, and want to spice things up in your "weed life". The little canisters of fluid give you a little flavor burst with every inhale. It's kind of like turning your bong into a quazi-hookah.
Imagine in your next smoke session you surprise your friends with flavored hits from your bong. They'll laugh from surprise and not just because they're faded. (Mostly because they're faded though.) I imagine you could also use this in a bubbler. If you try don't get any in your mouth, because it's "not for drinking".
Check your local smokeshop to see what flavors they carry, because BongWaterFlavours.com doesn't sell direct. If you can't find any in stores check online at http://www.shellshock420.com/catalogue2/index.php?productID=619