Why 8 -8oz glasses of water per Day

Dr. Chet says:

How Is 8 x 8 Justified?
Let’s get back to the original question of the eight 8-ounce glasses of water per day. Is it justified? Let's look at a basic physiology textbook, such as Guyton’s Textbook of Medical Physiology (1). You find in a section in the chapter on fluid balance that they talk about how much water we lose every day under normal conditions:

• Skin (not from sweat)--12 ounces
• Lungs--12 ounces
• Sweat--4 ounces (without exercise)
• Feces--4 ounces
• Urine--48 ounces
• Total: 80 ounces per day. And remember, that’s without sweating due to exercise or high heat and humidity.

The recommended 8 x 8 would provide 64 ounces, and that means we would be 16 ounces short based on typical fluid loss, even before your daily exercise routine. That’s why eight 8-ounce glasses of fluid per day is still a good idea. Notice I said fluid. Tea, coffee, sports and energy drinks, soft drinks, juice--all fluids count toward that total.

There’s one more thing that you’ll probably read somewhere and that’s the water in fruits and vegetables counts toward that total. I agree, but most of us eat only three or four servings of fruits and vegetables per day, if that. Let’s say you start your day with an orange; that’s four ounces of fluid. Later, with your dinner, you have a medium baked potato along with a cup of broccoli; that would add four ounces and three ounces respectively. Then let’s say you top it off with a banana--another three ounces. From the foods you ate, you got 14 ounces of water--you still need another 66 ounces. And that’s why eight 8-ounce glasses of fluid per day is still a good idea. Now you know why. Bottoms up!

References:

1. Guyton and Hall. Textbook of Medical Physiology. 10th Edition. W.B. Saunders. Pps 264-5. 2000.