The reason I use a hot water bottle is b/c it was recommended by my colon therapy office director. She doesn't like the thought of putting electric current on you. Interesting that this Cayce-related site doesn't seem to mind.
I used a hot water bottle last night. (It's not a bottle really -- it's more a large plastic pillow.) Putting my duvet over it acted like a tea-cosy and kept the heat of the water at a warmer-than-body-temperature level for the 90 minutes that I was under there.