Things in the Game: Water
With Rich's heavy backpack and load of diamonds, he will sink immediately if he fall into water. Spiders avoid water, but Robots and Bug-Eyes are not so clever.
Rocks will also sink in water, so if you roll one in, it's gone.
If you need to cross water, there are always those handy boxes. Ideal for floating on top of water, they make great stepping stones. Just remember, once they are in the water, you can't get them out. Also, other things can walk on them (like that spider that is chasing you!)