Park your car overnight and put a large white piece of paper underneath your car. In the morning check the paper. If the paper is wet with liquid, you could have a water pump leak.
If the paper has green (in most cases) fluid on it, there is a good chance your vehicle is leaking coolant (sometimes referred to as "water"). In many cases, when you are leaking coolant it could be coming from the water pump.
Turn the engine off and open the hood.
Locate the water pump pulley. The pulley is the round part that the belt is attached to. To find it, look for the belts. You will see more than one pulley. Your car will have an alternator with a pulley and perhaps an air conditioner, power steering and smog pump pulleys. If you are unsure, ask your mechanic to point out the water pump pulley.
Grab opposite ends of the round pulley and check for "play" (looseness): Try to rock it back and forth. There should be no give. If there is, the bearings are going and it's time to replace the water pump. By the time you can feel play in the water pump pulley, you may also be able to hear the bad bearing when the engine is running - there may be a low-pitched grinding noise coming from the water pump pulley.
Visually check the water pump (it's located behind the pulley) for signs of a coolant leak. If the water pump gasket is leaking, it must be replaced. This is a good time to get a new water pump, too, unless it was just recently replaced.