What could have caused a perfectly fine alternator on a 92 Accord to start squealing after the mechanic replaced a leaking water pump??

 

The belt tensioner is probably too tight. try loosening the tension and see how that works. best of luck.

 

he probably f***ed it up so you go back to get it changed which means $$$ for him.

But seriously... it could be the belt tension. A quick way to check that would be to spray a <U>short</U> burst of WD40 just above the belt so the mist just lands on it. (don't spray the belt literally!) if it stops the squealing it could mean the belt tension. If not then it could be the bearings in the alternator. i have no clue why that would happen after having the water pump changed because that is round the other side... unless the mechanic pulled a pipe that splashed coolant over it?