I keep fish for a hobby and was horrified to see a letter published in a well know caravan magazine suggesting the use of a fish tank heater to keep the water barrel ice free during winter use. These heaters are quite delicate and are designed to have only the appropriate part of the heater submerged in water. This would be difficult to achieve just hanging it by its flex into an aquaroll. I can assure you the safety instructions supplied with these heaters always clearly state for indoor use only.