You should always consult your water cooler user manual for cleaning directions. Most dispensers suggest using a citric acid crystal product to clean out mineral deposit build up. That being said, vinegar is a great natural product for loosening mineral built up and cleaning bacteria. Just be sure that if you use it to clean the internal workings of the water dispenser that you thoroughly flush with water. This will ensure that you don't get an unpleasant vinegar taste in your drinking water.