A bad bearing or seal shows up as coolant dripping/oozing from the seep hole on the botton of the pump. Noise would also be a sign.
I think I've once heard of an impellar failure, so I would not remotely think that is an issue. Bearing failure and afterwards seal failure are the most common issues.
Really, you'll know it (water leak) if it's needing replacement.
Good luck with the cooling system bud.