It seems much better to drop the bombs wherever than just to dump them in the water. I read an account of a German farm that got blown up. It did undermine morale, which used to be part of winning a war.
In the case of Glenn Millers disappearance, one explanation has it that his light plane got in the way of an RAF bomb dump.
My memory is fuzzy on this matter but I read that at some point in the war, the issue arose with either the USAF or RAF as to what to do with bombs that could not be released over German targets. The decision was to release over Germany.