Chug your 40oz: How To Stay Properly Hydrated

Written for by Jay Stadtfeld

I always laugh when people tell me they drink the recommended 8 glasses of water a day. Not because it’s bad advice (some water is better than none, and more is better than less), but because it’s very vague, FDA advice. And let’s face it, the FDA doesn’t get a lot of things right. This being no different.

I’ll be the first to admit that I don’t know what works for you. Perhaps 4 glasses, maybe even 80. But, what I can suggest without knowing you is that you’re probably not drinking enough water. If your joints ache, your head hurts, and you feel sluggish, drink more water before reaching for the nearest coffee pot. Your body is made up of roughly 60% water, so why not give it what it likes most?

I typically aim for (at minimum) two clear urinations a day, and is what I give beginner clients as a recommendation. You’d be surprised at the amount of water that can take, too. There are also a few means of increasing water retention, as well so as to avoid cramping during strenuous activity. Simply adding a pinch of salt to your water can improve your body’s ability to hold onto it and decrease cramping tendencies.

But uh… don’t drink this. K?

Basically, if you find your urine to be yellow and smelly, you need to drink more. Water is just as important (perhaps more-so) than any other substance you’ll put into your body.

Now, a little science coming your way.

Body water moves from areas of high solute concentration to areas of low solute concentration (i.e. more dilute) in order to maintain equilibrium in all body compartments.

Water provides the medium for the solubility and passage of nutrients from the blood to the cells and the return of metabolic by-products to the blood. Countless metabolic reactions in the human body rely on water as a medium.

Sensible body water loss (i.e. water loss that we know is occurring) occurs daily in the stool (200 mL), urine (500 to 1500 mL) and sweat. Insensible losses (i.e. those we can’t perceive) occur through the skin (500 mL) and respiratory tract (400 mL). These vary with humidity, environmental temperature and respiratory rate.

The hypothalamus, the renin-angiotensin-aldosterone system, and the kidney are responsible for fluid balance. Anti-diuretic hormone (ADH) and aldosterone are hormones that work with these systems to balance fluid volume. ADH is a water-conserving hormone. Aldosterone stimulates sodium and water retention. The chief stimulus for aldosterone secretion is sodium depletion and associated loss of plasma volume.

Hormonal regulation of body water

When body water changes, it can have significant effects throughout the body, including athletic performance. Indeed, dehydration of as little as 1% body weight (2 lb for a 200 lb person) is enough to reduce both endurance and strength performance — as well as cognitive performance.

What you should know

During exercise, we need more water. The enhanced metabolic rate of muscle contraction requires a larger delivery of nutrients and oxygen along with faster waste and heat removal from the body. Exercise is not the only situation that causes alterations in body water. During growth and development, the percentage of body weight that is water and the percentage of water outside and inside of cells do not remain constant. When expressed as a percentage of body weight, body water decreases during gestation and early childhood, attaining adult levels by around 3 years of age.

So where do we get fluids to maintain balance? Well, remember that water intake doesn’t come only from drinking water. It also comes from tea, coffee, non-dairy milks, milks, and water from solid foods. With thirst as a guide, humans are generally well hydrated. There is extreme variability in water needs based on climate and physical activity levels. Lab screening that qualifies someone for dehydration:

  1. Osmolality (serum) >295 mOsm/Kg H20

  2. Sodium (serum) >145 mEq/L

  3. Albumin higher than normal

  4. BUN elevated

  5. BUN:Creatinine ratio >25:1

  6. Specific gravity >1.031

In the clinical setting, dehydration can be detected by loss of skin elasticity or turgor. If a fold of pinched skin returns to its original shape especially slow (called tenting), then dehydration is suspected (see image below). Conditions such as vomiting, diarrhea or intestinal drainage can also cause fluid imbalances.

However, while dehydration is a concern, overhydration is also something to watch for when planning fluid replacement. Hyponatremia is an electrolyte disorder in which plasma concentrations of sodium fall too low. This is associated with neurological morbidity and mortality. Most cases of hyponatremia are induced by an increase in total body water. This is indicative of impaired free water clearance by the kidneys. Many instances of hyponatremia have occurred because of overdrinking water. For example, as the New England Journal of Medicine reports in a study of Boston Marathoners:

Hyponatremia has emerged as an important cause of race-related death and life-threatening illness among marathon runners… The strongest single predictor of hyponatremia was considerable weight gain during the race, which correlated with excessive fluid intake.

Make sure to stay properly hydrated all day. If you are thirsty, then drink some water. It’s that easy!


Borer KT. Exercise Endocrinology. Human Kinetics. Champaign, IL. 2003. Mahan LK & Escott-Stump S. Eds. Krause’s Food, Nutrition, & Diet Therapy. 11th ed. Saunders Publishing, Philadelphia, PA. 2004. Groff JL & Gropper SS. Advanced nutrition and human metabolism. 3rd Wadsworth Thomson Learning. 2000. ed. Murray RK, Granner DK, Mayes PA, Rodwell VW, eds. Harper’s Illustrated Biochemistry. 26th ed. McGraw Hill. 2003. Barnard ND, et al. Nutrition Guide for Clinicians. 1st ed. PCRM. 2007. Tufts University Health & Nutrition Letter. April 2004. Groff JL & Gropper SS. Advanced nutrition and human metabolism. 3rd Wadsworth Thomson Learning. 2000. ed. Thibodeau GA & Patton KT. Eds. Anatomy & Physiology, 4th ed. Mosby, Inc. St. Louis, MO. 1999. Beers MH, Berkow R eds. Merck Manual. 17th ed. Merck Research Laboratories. Whitehouse Station, NJ. 1999.

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