In regular cold tap water the effect won't last very long. What you can do is put a small crock pot in the bottom of the barrel keeping the water hot then dropping in the dry ice as the effect wains. Unfortunately the effect lasts only about 20 minutes or so then you have to drop in more dry ice. I once bought a large block and kept it in the crock pot in a cauldron and it worked pretty good. ..... cheers Scruff'