8 Glasses of Water per Day: Says Who?

From Gillian Mayman:

The idea that you need to drink at least 8 glasses of water a day is ubiquitous in American culture. I’ve had doctors tell me this. I’ve read it on credible medical web sites. I’ve listened to a professor of public health discuss this as if it is scientific fact.

However, there is no scientific basis for the “8 glasses of water a day” rule. Even more intriguingly, the origins are somewhat of a mystery….

Dr. Frederick J. Stare wrote a book in 1974 with Dr. Margaret McWilliams that contains one of the earliest known references in print to this admonition…..

However, what Dr. Stare actually wrote was:

“How much water each day? This is usually well regulated by various physiological mechanisms, but for the average adult, somewhere around 6 to 8 glasses per 24 hours and this can be in the form of coffee, tea, milk, soft drinks, beer, etc. Fruits and vegetables are also good sources of water.“…

The origins of the “8 glasses of water a day” rule was explored by Dr. Heinz Valtin in a 2002 article and Dr. Tsindos  in a 2012 article. After extensive searches of the published literature, they found absolutely no scientific evidence for the idea that most people need to drink at least 8 glasses of water a day.

So how much water do we need? Clearly, athletes and people who live in very hot climates need more water. But for the average person, the amount of liquid that they take in just needs to match the amount that they lose through bodily excretions such as urine, feces, sweat, and exhaled water vapor. For women this is about 2.2 liters and for men it’s about 3 liters, according to the Mayo Clinic. [This translates to about 74 ounces for women and 101 ounces for men.]  However, the liquid that is consumed does not need to be water. It can be tea, coffee, soda, juice or other beverage. It can also come from foods that we eat which contain water.