If you have chatted with a Naturopath lately, you have probably been told that you should take your body weight in pounds, convert it into ounces and divide it by 2 in order to find out how much water you should drink in a day. This is an attempt to deal with the fact that larger people obviously need more fluids than smaller people. (Of course, they also need more food than smaller people.)
Where I run into trouble with this is when I mention this to women who are obese. For example, let's say a woman is five feet four inches tall and weighs 200 pounds. This woman would discover that she should be drinking 12.5 glasses of water a day! If she is only drinking a couple of glasses now, she probably won't even try to increase her fluid intake if she thinks she has to drink more than 12 glasses a day.
Another view on this was in an article in the American Journal of Clinical Nutrition (2006;83:529-42) which stated that women should drink 8.9 glasses of fluids a day and men should drink 12.5 glasses of fluids a day. Well, it's true that women, on average, are smaller than men, on average. But what would I tell a large woman? Or a small man?
So the eight 8 ounce glasses of fluids a day at least has simplicity going for it. Unless you are a very small person, it should probably be considered a minimum.