Drink at least eight glasses of water a day. If you wait until you’re thirsty to drink, you’re not drinking enough. Drinking water between meals helps you lose weight. Hydrate, hydrate, hydrate.

We’ve had this advice drummed into our heads by certain elements in the medical community and (to a much greater degree) by the bottled water industry over the last few years to such an extent that few of us probably doubt its validity. Luckily, there are always a few skeptics among us who hear things like this, wonder if it’s really true, and check the facts. In this case, a professor from Dartmouth medical school looked into the cult of water drinking and found that the evidence supporting the health benefits of drinking eight glasses of water a day is sketchy at best.

Dr. Heinz Valtin undertook an exhaustive search for hard scientific evidence that the health of average people is improved in some substantial way when they consume the recommended 64 ounces of water a day, and about all he could really conclude was that such excessive water consumption leads to more frequent trips to the restroom and a healthier bottom line for the bottled water industry.

The misunderstanding about how much water a healthy person needs to consume apparently stems from a 1945 report by the Food and Nutrition Board that said that the body needs about 1 milliliter of water for each calorie consumed. This was translated into the ubiquitous eight glasses of water a day recommendation. But such an interpretation fails to account for the fact that the food that we eat contains a great deal of water and therefore provides our body with much of the water it needs.

Fruits and vegetables are 80 percent to 95 percent water. Meat contains a good bit as well. Even dry bread is about 35 percent water.

There is also little evidence that drinking a lot of water between meals helps anyone lose weight. Although drinking a lot of water with your meal may help you feel full faster and eat a little less, drinking between meals apparently has little effect on appetite.

So if we don’t really need to chug eight bottles of Evian every day, how do we know how much water we should drink to stay healthy? Well, it’s pretty complicated. Go get paper and pencil (and possibly a calculator if your arithmetic skills are not particularly strong) and I’ll give you the new formula.

OK, ready? Here it is. You should drink when you are thirsty. If you aren’t thirsty, you can stop drinking. Exceptions should of course be made for people with certain exceptional health conditions (like kidney stones) or for anyone who is about to engage in strenuous exercise. And elderly people sometimes lose their appetite and sense of thirst, so their fluid intake needs to be monitored.

For the rest of us it’s pretty simple get thirsty, drink, go to the bathroom, repeat. Not a particularly impressive marketing slogan for the bottled water companies, but I’m sure they’ll find a way to adapt. They always do.

Bill Ferguson is a columnist for the Warner Robins (Ga.) Daily Sun.