Was it a metal or a plastic 55 gallon drum? Either way, it was probably going to be used for water, but I shudder to think what it previously contained. The plastic ones, in my thinking, are usually safer because they are not used to carry volatile or hazardous liquids.
Although tempting, I prefer not to "borrow" when something is available for sale, even if I cannot afford it. It's a personal hang up of mine which makes many people think I am strange.