The Mythical Daily Water Requirement

By Mike Howard

daily water requirement8 glasses – that’s what most people think they need as a daily requirement.

Copious water intake is supposed to keep organs functioning properly, skin supple and body weight at bay.


Say researchers from the University of Pennsylvania who conducted a study to test these theories (which will be published in the June issue of the Journal of the American Society of Nephrology).

We all know that our bodies need water, but nobody quite knows exactly how much. Let’s take a look at where this misconception began, shed some light on water and hydration and look at some more realistic water goals.

Let’s be clear on something right out of the shoot. Water is the hub of all chemical processes in the body and the king of all nutrients. We should be drinking it daily.

Where did the 8 glasses/day gospel originate?

Dr. Frederick Stare suggested this theory in a book “Nutrition for Good Health” published in 1974 (“theory” being the operative word). The theory caught on despite its arbitrary origins and it has been speculated that bottled water companies are largely responsible for perpetuating the 8-a-day mantra.

Water Intake – Not Just From Water

Counter to what I’ve just presented, we actually DO need at LEAST 8 glasses of water per day.

But here’s the catch: This intake is satisfied not only from water intake, but also from other fluids, the food we eat and the metabolic processes required to break down that food.

water in foodsJuice and milk contribute to hydration and (surprisingly enough) so do caffeinated and alcoholic beverages. I probably don’t have to tell you though, that alcoholic beverages are not recommended to help you meet your fluid requirements.

Regarding caffeine – many people still believe it causes dehydration, however studies as early as 1928 have shown otherwise.

The fluid from food and its accompanying metabolic action alone can account for as much as 6 glasses of water! Water is the best fluid – no argument there, but don’t get caught up in the absurdity of forcing down extra glasses of water if you have a coffee.

Water – Too Much of a Good Thing?

The more the better does not apply to even the mighty water. Consider that 31 runners in the 2000 Houston Marathon were treated for hyponatremia – a condition that can arise with excess fluid consumption, causing a dilution of sodium in the blood.

This has prompted a revision of previous guidelines which have changed from “drink as much as you can tolerate” to “drink as needed, but do not exceed 800ml per hour”

Estimating Water Needs

  • There is a large variation when it comes to individual water needs. Those who are active have increased water requirements, especially if exercising in hot weather.
  • As a baseline, 1L of water a day (about 3 glasses) should be fine for those individuals who are relatively sedentary.
  • Increasing water intake to 1.5-2.5L/day (4-5 glasses) per day is a good idea if you are moderately to highly active, and drink a few gulps every 15-30 minutes if exercising in hot weather.
  • If you are exercising for longer periods of time (going on a long hike, as an example), be sure to consume some salt when consuming large quantities of water.
  • If fat loss is your goal, make water your primary beverage – aim for 75% of your fluid consumption, while cutting back on juice, pop and other calorie-containing liquids.

In Closing

Let’s face it, most of us would probably benefit by drinking more water for the simple fact that it replaces other caloric and otherwise unhelpful fluids.

Drink water whenever you can – try to have a glass with each meal, and consume it while you are exercising. Use common sense when hydrating during exercising – especially in hot weather.

You need not, however count empty bottles, or stress if you fall a glass or two short of your daily “requirement”.

How much water do you drink?


  • Stare, FJ, and McWilliams M. Nutrition for Good Health. Fullerton, CA: Plycon, 1974, p. 175
  • Grandjean, AC, Reimers KJ, Bannick KE, and Haven MC. The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration. J Am Coll Nutr 19: 591-600, 2000.
  • Tufts University Health and Nutrition Letter. New Consumption Guidelines for Water Sodium, Potassium. April, 2004
  • THE PHYSICIAN AND SPORTSMEDICINE – VOL 31 – NO. 7 – JULY 2003. New Hydration Recommendations.
  • Casa DJ: Proper hydration for distance running: identifying individual fluid needs. Available at
  • Weinberg, A, and Minaker K. Council of Scientific Affairs, American Medical Association: dehydration evaluation and management in older adults. JAMA 274: 1552-1556, 1995


  1. Jason

    Umm. Hate to nitpick, here, but you have a post about scientific research that is upcoming and you’re talking about a lot of science, but the comment about (“theory” being the operative word) betrays a misunderstanding of what the word “theory” means in a scientific context. Honestly not trying to be a pain, but you might want to think about using a different word.

  2. Ryan

    Wuh-oh. I hope that the “newfound evidence” of drinking too much water isn’t true. I myself drink about 3 liters of water a day, don’t know why, and I weigh only 162 lbs. I think that drinking too MUCH water at once may have immediate negative effects on sodium dilution and such, but as long as you space out your drinking enough so that your body can get rid of the extra water, the overall amount you can drink per day is practically unmetered.

  3. Davey

    I started drinking good water on a regular basis 15 months ago and this is the second winter I haven’t had to use chap stick ! I detoxed a bit with alkaline water the kind which is micro clustered (gets into cells easier) and it help me with my arthritis. It help me get rid of shoulder pain from accident 7 yrs. ago. The ‘cracking’ in my neck.My mood is better. Energy is up. I ‘grew’ taller (by hydrading my discs). I asked the nurse to dbl check my ht twice @ last physical Most of my back pain is gone. I’m surprised author said coffee doesn’t dehydrate you. I have to run to bath rm several times after drinking coffee. I like to drink @ least 128oz+ per day. Also my skin looks & feels better. I’m very happy since I hydrated my body!

  4. Atul

    Thanks for the information. I have become an avid green tea drinker, more than 2 litres a day, and lost weight just due to this. I reduced my normal intake of water and have wondered why it never affected me.
    I always drink less than a litre of warm water first thing in the morning and shoot to the loo. But through the day my intake of water has reduced.

  5. Michael

    He said 8 glasses, not 8 cups, which is a huge difference. How big is a glass? We know a cup is 8 ounces. A glass can be 6 to 12 ounces. If you drink 8, 12 oz, glasses, you could be getting 100 ounces a day.

  6. Michael

    He said 8 glasses, not 8 cups, which is a huge difference. How big is a glass? We know a cup is 8 ounces. A glass can be 6 to 12 ounces.

  7. Michael

    This article is confusing people by using the phrase ‘8 glasses’.

    What you should be aiming for is 8 CUPS a days. Meaning that you should be counting cups as in an official measurement and not just a glass in your cupboard. Even better is to count the number of ounces. There are 8 ounces in a cup. If you drink 8 cups, you are getting 64 ounces. If you drink 8 glasses, you could be getting 100 ounces a day and not realize it.

    Do you drink from water bottles all day? Did you know that each bottle is 2.5 servings or 2.5 cups or 20 ounces?

    You really need to pay attention to the VOLUME and not the number of random containers.

  8. Mavis

    I am a diabetic who has had a heart attack at 30, a triple-bypass at 40, a stroke at 48 (whick took most of my sight), and a quadruple bypass at 52. I also suffer from fibromyalgia, and was an undiagnosed diatetic for 20years or so. Our generation was the first to experience “soda pop” and all the drinks that came after. Needless to say, I’m sure that if I had drank more plain water, some of these things might not have presented so early, or maybe not even so hard. I’ve been disabled for 12 years now, and am still suffering from the poor eating and drinking habits I used to follow. Good luck to all!!!

  9. Sam

    Believe it or not drinking a lot of water regularly made me feel physically and mentally better, no matter what my diet was like. It’s a panacea for most common maladies like hangovers, illnesses etc. I drink at least 2.12 litres a day but don’t be afraid to drink a bit can only do good.

  10. sarah butterfield (mrs)

    I find this ‘you must drink 8 glasses of water a day’ advice boring! boring! boring! The amount of water each of us needs to drink varies from person to person. Not only that I watched a programme recently called ‘should I worry about water’ presented by Richard Hammond. And I was pleasantly surprised to learn 8 glasses of water a day was unnecessary. Check out the website for yourselves and you’ll be surprised and hopefully it’ll stop you all making yourselves feel bloated and miserable by forcing yourselves to drink an amount of water that you probably didn’t need to drink in the first place. Unless you feel comfortable doing so.