So I have a 94 B250. She's awesome. This morning I discovered my serpentine belt had slipped off. After putting it back on and turning the engine over I find that it starts to slip off the crank. I am also now having water drip out of the water pump. The pump isn't seized. Do I have a bad water pump?
I was also wondering what parts might be interchangable.

 

Yes, your water pump is bad. What do you mean by, "interchangeable part"?

 

The leak is due to the water pump shaft being worn, the wear also allows the shaft to be cocked to one side. With the shaft being off like that the pulley is no longer running straight so the belt eventually works it's way off. Replacing the water pump should fix both issues.

 

Water pump and if that doesn't fit it, belt tensioner afterward.
Don't do the tensioner first.

Check that belt is not damaged.