Obviously, water is not a myth, but there are two main myths or misconceptions that abound: 1) you need at least eight glasses of water a day, and 2) only water hydrates you.

1) You need at least eight glasses of water a day

Proper hydration is required to flush toxins from vital organs, carry nutrients to your cells and a host of other things. However, the question is, how much do we need? The ‘eight glasses a day’ is a recommendation that is seen a lot, including here.

It is not completely clear where the 8 glasses a day came from, but there is no evidence to support the requirement.

Heinz Valtin did an extensive review of this recommendation, which was published in the American Journal of Physiology (http://ajpregu.physiology.org/content/283/5/R993.long). He concluded that there is lack of any evidence supporting the eight glasses a day. “I have found no scientific proof that we must “drink at least eight glasses of water a day,” nor proof, it must be admitted, that drinking less does absolutely no harm. However, the published data available to date strongly suggest that, with the exception of some diseases and special circumstances, such as strenuous physical activity, long airplane flights, and climate, we probably are currently drinking enough and possibly even more than enough.”

In fact, in extreme circumstance, drinking excessive amounts of water can actually be dangerous, resulting in hyponatraemia (water intoxication).

So how much water, or other fluids, should you drink a day? That depends on your personal circumstances including how active you are, climate, how much fluid you get from your diet and your general health. The following is a quote from the Mayo Clinic: “Generally if you drink enough fluid so that you rarely feel thirsty and produce 1.5 liters (6.3 cups) or more of colorless or light yellow urine a day, your fluid intake is probably adequate. If you're concerned about your fluid intake or have health issues, check with your doctor or a registered dietitian. He or she can help you determine the amount of water that's right for you.”

2) Only water hydrates you

The simple answer is that you can obtain fluids for hydration from beverages and food. It is not just plain water that hydrates you and caffeine is basically no more a diuretic than water is unless consumed in large quantities, and even then, the diuretic effect is minimal. You do obviously have to count the calories in your beverages/food.

For the geeks, or if you do not believe me:


http://www.mayoclinic.com/health/water/NU00283 - any beverage counts

"beverages such as milk and juice are composed mostly of water. Even beer, wine and caffeinated beverages — such as coffee, tea or soda — can contribute"

"What you eat also provides a significant portion of your fluid needs. On average, food provides about 20 percent of total water intake."


http://www.jacn.org/content/22/2/165.short flavored plain water counts

"Inclusion of plain drinking water compared to exclusion of plain drinking water in the diet did not affect the markers of hydration used in this study."


http://www.jacn.org/content/19/5/591.short any beverage counts

"This preliminary study found no significant differences in the effect of various combinations of beverages on hydration status of healthy adult males. Advising people to disregard caffeinated beverages as part of the daily fluid intake is not substantiated by the results of this study."


http://bjsportmed.com/content/40/5/406.abstract sports drinks can hydrate more than plain water in some situations

"Ad libitum consumption of a CHO-E drink may be more effective than water in minimising fluid deficits and mean core temperature responses during tennis and other similar training in adolescent athletes."


http://www.jacn.org/content/26/suppl_5/592S.short food counts

"Various reports indicate that humans receive 20–25% of their daily water intake from food. Fruits, vegetables and other high-moisture foods, therefore, make an important contribution to total fluid intake."


http://europepmc.org/abstract/MED/12834577 the diuretic effect of caffeine is minimal

"...nor does it cause significant dehydration or electrolyte imbalance during exercise."


http://europepmc.org/abstract/MED/12187618 the diuretic effect of caffeine is minimal

"The literature indicates that caffeine consumption stimulates a mild diuresis similar to water, but there is no evidence of a fluid-electrolyte imbalance that is detrimental to exercise performance or health"

"Investigations comparing caffeine (100-680 mg) to water or placebo seldom found a statistical difference in urine volume."


http://jap.physiology.org/content/83/4/1152.abstract? interesting one about alcohol post exercise and recovery

“There appears to be no difference in recovery from dehydration whether the rehydration beverage is alcohol free or contains up to 2% alcohol, but drinks containing 4% alcohol tend to delay the recovery process.”



In the interest of clarity, this post is not intended to encourage people not to drink water – it has zero calories and is free/cheap, but to try to clear up any misunderstandings with regard to hydration.