How can you tell if water pump is going bad?

Occasionally they will fail without previous symptoms.

BUTTo check

1. Look at the weep hole on the bottom of the pump behind the pulley. You may need a mirror. If there is a dribble line or any coolant coming out its toast.
2. Remove the drive belt and see if the bearings allow any side to side or up down movement, if you feel any, its toast.
3. Hold it and turn it back and forth, repeat until you have felt all of the bearing, any sound or roughness it needs replacement.