There are two ways to check the water pump's functionality without removing it from the engine. A defective pump must be replaced with a new or refurbished one.
The water pump is equipped with control (or ventilation) holes (see illustration below).
If the seal fails, coolant will start leaking from the holes. Get a flashlight and a small mirror, then remove the timing belt cover. Use the flashlight and mirror to locate the inspection holes at the bottom of the rear of the pump and check to see if any coolant is leaking from them.
When the pump shaft bearings fail, a howling sound may be heard at the front of the engine while it is running, which should not be confused with the whistling sound made by the drive belt when it is released. Bearing wear can be detected by the presence of play when the pump pulley is rocked (don't forget to turn off the engine first).