How do I know if my water pump needs replacement?

It's common if you don't perform the preventive maintenance required. You have a leak. Coolant doesn't evaporate. If you had to add a half gallon of coolant you have a leak. Sometimes water pumps leak only hot or running. If there was a presence of coolant at the weep hole on the water pump then you need a water pump. The water pump is timing belt driven. It's about 5 to 6 hours to replace. What else do they want to replace with the water pump. It's 6 years old. If it was my truck I would replace the timing belt to. Just because of age not mileage. A timing belt is rubber. Rubber has a age life in addition to a mileage life. I agree with PARTS GUY. You need to check all your fluids at least once a week. Takes about ten minutes.

a small leak now may be a large leak very soon. I would be pro active and get it replaced before it lets you down. Roy