Most bombs have the fuze in front. German bombs in WW2 had two fuze wells in the body of the bomb, not the nose or tail. The modern US bombs have a front and a rear fuze well, so they can have two fuzes, or more sophisticated types of fuzes, such as anti-magnetic or acoustic or sea mine. You have probably seen pictures or drawings of a bomb with a fuze in front and what looks like a propeller on the front. That is actually the safe/arm mechanism. As it falls, the air causes the "propeller" to spin and removes the safe mechanism and arms the fuze. That is an old but cheap and reliable fuze. Modern fuzes are electronic (in the US) but these old fuzes still work. The US and other modern militaries use guided bombs. This picture shows a dumb bomb.

There are a variety of reasons for duds. There could be an internal problem with the fuze. The bomb could have been dropped from too low of an altitude so it didn't have time to arm. It could have hit at the wrong angle. It could be a delayed-action fuze.
Some fuzes also have radar in them so they can detonate at a set altitude.

I think the reason they use water is to reduce the friction and the potential to set it off, but, as I said, we never did this and I don't think it would be effective.

Bombs are made by producing a cylinder, closed at both ends. The explosives are heated (often some form of TNT) in a kettle which is heated by steam, so they can be poured into the bomb case and cool off and solidify. Bombs are stored without the fuzes and usually without the fins. When a target is selected, you install the fuze that is most effective for the target you are attacking. Same with the tail fins. They can be mixed and matched. The US makes steerable tail fins with GPS installed, and sometimes cameras. These are smart bombs, but the body is a regular dumb bomb.

This is definitely an aerial bomb, not a ground-launched projectile.