I've recently started wrenching on a friend's integra 1.8 because he thought the water pump had gone out and he had some one start the process of tearing it down then ended up with some law trouble so I took over ...after removing the old water pump I can see no clear mechanical failure the impelar is in tact and everything seems to be fine my question is could a water pump appear to be mechanical sound but still be faulty?

 

in a nutshell, no. if you dont see anything obvious, and there's no play in the bearings, and no evidence of the pump leaking, 99.9% chance the pump is still good.

why did he think the pump was bad?