The old thought is that you are suppose to drink 8 glasses of water a day. We think that’s a good place to start, but to find out for sure we’ve provided you with a water calculator! Age, health and activity level all play a part on how much water you should drink a day. Try it out: http://www.mayoclinic.org/healthy-living/nutrition-and-healthy-eating/in-depth/water/art-20044256