How much does my camera rig weigh underwater?

Tired of having a negative rig that is hard to control underwater? There are many good reasons for having a neutral/slightly negative rig. If like myself you do not have an endless supply of money to keep buying equipment to try and get the right balance or little access to a pool you need to find out your starting point.
By understanding the exact weight of your camera rig underwater you can then work out what best to do next.