In the case of your rat, I would have looked for a shovel or similar tool with a long handle to scoop him out of the water. I'm not much of a fan of mice and rats, but I wouldn't want to just let it drown, either. There are traps designed as bucket lids which pivot suddenly when they go for bait in the middle, drop them into water, and trap them there to drown. It's not as messy as other traps, but it does seem cruel. Then again, we have cats for pest control, and that isn't exactly a guaranteed swift death for the rodents, is it?