Col. Jeff Cooper USMC gave us the four rules as follows:

All guns are always loaded. Even if they are not, treat them as if they are.

Never let the muzzle cover anything you are not willing to destroy. (For those who insist that this particular gun is unloaded, see Rule 1.)

Keep your finger off the trigger till your sights are on the target. This is the Golden Rule. Its violation is directly responsible for about 60 percent of inadvertent discharges.

Identify your target, and what is behind it. Never shoot at anything that you have not positively identified.   
You can even check out the Wikipedia page in Gun Safety and search for the word water or shooting over water or into water and you will find nothing, but if you look on the back of your newly bought cartrige box you will fin explicit instructions to not fire into or over a body of water. 
 From the local news station we learn of a guy as the story says: "A sheriff's report says the man told deputies he fired a shot into the Deschutes River on Sunday afternoon but the bullet ricocheted off a rock and hit him in the temple. When he scratched the spot with his finger, he says the bullet fell out of his head and into the river." We what was behind this guys target was a rock. I don't know how many times I have been shooting along the canals in Yuma, AZ or in my back yard into the pond when I lived in the woods, so this gives us all something to think about and and if you don't think its real or predictable, here is an example of how predictable a ricochet could be:


Happy and safe shooting everybody!!!!