Oldsmobile/Buick Repair: 93 century water pump replacement, water pump replacement, radiator hose

Question
as i was driving today i heard a clunk and the alternator light came on so i figured i had thrown the serpentine belt on my engine. i was surprised to find that however the fact of the mater was that the belt pully from the water pump had fallen off.  it apears to be the push on style, there are no keepers or bolts or anything like that to keep it in place.  so i was wondering what would cause this pully to fall off, and if in fact it has fallen off because the water pump is bad how hard is it to replace the water pump on my own.  also what is the best or reccomended way of making sure that the pully is back on and tight enough on the exisiting water pump or on the new one so that is doesn't fal off again?  thank you.  the car info is a '90 buick centurey with a 3.3 litre fuel injected engine.  also it has A/C.

Answer
Hi,Josh

Usually the water pump pulley is held on by 4 small bolts to the water pump drive,on the 3.3liters ive never seen the pulley pressed on,the only pulley that is a press on design is the power steering pulley,if in fact it is the water pump that is failed,it can be easily replaced,check into this further,the water pump is located in the ft portion of the engine it has the lower radiator hose connected to it,let me know.Thanks

ED