Actually its a great thing to do if you dont have barrel treatment, because it cuts the oil and other goo on the outside of your paintballs which messes up good barrels. Thats why I told people to rub a paper towel on their balls before playing, because it takes off most of the oily residue. Hot water works best, usually what I do is run the water through my barrels then get a paper towel and just put the barrels upright for a while on the paper towel, the gravity brings all the water to the paper towel. So actually its a good thing.