Proper hydration is key to good health, but why? And what’s the best way to get what our bodies really need? Our experts debunk a few myths. 

Water is the body’s most non-negotiable nutrient. Withhold any other vitamin or mineral for a week or more and the body will plug along. But deny it water for a mere three days and systems start to crash. Without water, the blood thickens and the body’s enzymatic processes — normally zipping along — get bogged down. Hold back another few days and the blood gets so gummy that the body’s inner workings grind to a halt. After that, odds of survival are grim.

Why is there so little wiggle room when it comes to water? Because water plays an integral role in nearly every biological process in the body. Everything from controlling the body’s thermostat to regulating blood pressure to taking out the trash relies on water to get the job done. Yet, for such a life-and-death nutrient, most of us take water for granted. Sure, we know we should imbibe, but how much? Does the water in caffeinated drinks, like coffee and soda, count for or against us? And should you drink before you’re thirsty or wait for your thirst signal to kick in?

“A lot of what we think about water is sheer guesswork,” says Elson Haas, MD, an integrated-medicine physician in San Rafael, Calif., and the author, most recently, of Staying Healthy with Nutrition (Celestial Arts, 2006). “A lack of research has led to a lack of knowledge. In fact, most of what people think they know about water isn’t even true.”

To get beyond confusing water myths and delve into some commonsense wisdom, we tapped several experts on water intake and human health. Here are the ins and outs of keeping your body well watered.

Myth No. 1: Dehydration is relatively rare and occurs only when the body is deprived of water for days.

Reality: Low-grade dehydration (versus acute and clinical dehydration) is a chronic, widespread problem that has major impacts on well-being, energy, appearance and resiliency. Christopher Vasey, ND, a Swiss naturopath and author of The Water Prescription (Healing Arts Press, 2006), believes that most people suffer regularly from this type of chronic dehydration because of poor eating and drinking habits.

While chronic dehydration does not directly result in death, “the lack of water results in a general weakening of the body’s internal cellular environment,” says Vasey, which can give rise to a number of health problems. For example, chronic dehydration can cause digestive disorders because our bodies need water to produce the digestive juices that aid the digestive process. If we don’t get that water, we don’t secrete enough digestive juices, and a variety of problems — such as gas, bloating, nausea, poor digestion and loss of appetite — can ensue. (For more health problems that can result from chronic dehydration, including energy loss, respiratory troubles, skin problems and obesity, see “Why Water Matters.”)

Bottom Line:If you’re not actively focusing on hydrating throughout the day, there’s a good chance you could be at least somewhat dehydrated, which could be negatively affecting your energy, vitality and immunity — as well as your appearance. Experiment with drinking more water throughout the day. You may observe an almost immediate difference in your well-being, and even if you don’t, establishing good hydration habits now will do many good things for your cellular health over the long haul.

Myth No. 2: Your body needs eight, 8-ounce glasses of water daily.

Reality: Your body does need a steady supply of water to operate efficiently and perform the many routine housekeeping tasks that keep you healthy and energetic. So it’s probably a very good idea to consume moderate quantities of water at regular intervals.

That said, there is no scientific evidence to back up the very specific and well-worn advice that you need to drink eight, 8-ounce glasses of water a day (a.k.a. the 8 x 8 rule). In 2002, Heinz Valtin, MD, a retired physiology professor from Dartmouth Medical School and author of two textbooks on kidney function, published the definitive paper on the subject in the American Journal of Physiology. He spent 10 months searching medical literature for scientific evidence of the 8 x 8 rule only to come up empty-handed.

In 2004, the Institute of Medicine (IOM), a division of the National Academy of Sciences, actually set the adequate total-daily-water intake at higher than 64 ounces — 3.7 liters (125 fluid ounces) for men and 2.7 liters (91 fluid ounces) for women. But those numbers refer to total water intake, meaning all beverages and water-containing foods count toward your daily quota. Fruits and veggies, for example, pack the most watery punch, with watermelon and cucumbers topping the list.

But the “it all counts” dynamic cuts both ways. Vasey believes that many people suffer from low-grade, chronic dehydration because of what they are eating as well as what they are drinking. The “I don’t like water” crowd could probably make up their water deficits by eating the right kinds of foods, he asserts, “but most don’t eat enough fruits and vegetables. Instead they eat meat, cereals and breads, which don’t have much water and contain a lot of salt.”

Animal proteins require a great deal more moisture than they contain to break down, assimilate and then flush from the body. And many processed foods, such as chips and crackers, for example, are nearly devoid of moisture, so — like dry sponges — they soak up water as they proceed through the digestive system.

A second strike against refined foods is the salt factor. Most processed foods, especially cheese and cold cuts, are packed with sodium. The body requires only 3 to 5 grams of salt a day to stay healthy, but most people gobble up 12 to 15 grams of the stuff daily. To rid itself of the overload, the body requires copious amounts of liquid. So you have to weigh your personal intake thoughtfully.

“Some people drink plenty of water, but the majority don’t,” Vasey says. To counteract anything resembling a standard American diet, says Vasey, “you must drink more.”

Bottom Line: If you want to stay optimally healthy, hydrated and energetic, it’s a good idea to eat plenty of water-containing foods and drink water throughout the day. And when in doubt, it’s probably not a bad idea to make a point of drinking a little more water, rather than a little less. But that doesn’t mean you need to down eight glasses exactly, or that if you run a little shy of 64 ounces, then something awful is going to happen. Just be aware that the fewer vegetables, fruits and legumes you are eating, and the more dried, processed or chemical-laced foods you include in your diet, the more water you’ll need to consume to compensate.

Myth No. 3: When it comes to hydrating, all beverages are created equal.

Reality: Not so. In principle, the 90 to 125 (or so) ounces recommended by the Institute of Medicine would include your morning coffee, the soda you drink with lunch and even a glass of wine at dinner. Practically speaking, however, caffeinated, sweetened and alcoholic drinks pack chemical cargoes (or trigger chemical reactions) that demand significant amounts of fluid to properly process and filter. As a result, nonwater beverages can actually set you back, water-wise, many experts suggest. “They can actually dehydrate the body,” says Haas.

For example, says Vasey, drinks like coffee, black tea and cocoa are very high in purines, toxins that must be diluted in large quantities of water to be flushed from the body. “The consumption of these drinks might bring a large quantity of water into the body, but a large portion of this water is used to eliminate the toxins in these drinks,” he says.

Artificially sweetened drinks add to the body’s toxic burden. Sugar and coffee also create an acidic environment in the body, impeding enzyme function and taxing the kidneys, which must rid the body of excess acid.

Moreover, says Vasey, caffeine found in coffee, black tea and soft drinks adversely affects your body’s water stores because it is a diuretic that elevates blood pressure, increasing the rate of both the production and elimination of urine. “The water in these drinks travels through the body too quickly,” says Vasey. “Hardly has the water entered the bloodstream than the kidneys remove a portion of the liquid and eliminate it, before the water has time to make its way into the intracellular environment.” (For more on the importance of intracellular hydration, see “Myth No. 5.”)

Bottom Line: Don’t think you can toss back a few cans of Red Bull and call it a day. Moderate consumption of beverages like coffee and tea is fine, but be aware that while some of the fluids in nonwater beverages may be helping you, certain ingredients may be siphoning away your body’s water stores. So, when you’re drinking to hydrate, stick primarily with water. And, if you’re looking for a pick-me-up, try sparkling water with a squeeze of citrus.

Myth No. 4: By the time you get thirsty, you’re already dehydrated.

Reality: Again, it depends on what you mean by “dehydrated.” Experts like Vasey posit that while those walking around in a state of subclinical dehydration may not feel thirst, their bodies are sending other signals of inadequate hydration — from headaches and stomachaches to low energy to dry skin.

But when it comes to avoiding the more widely accepted definition of clinical dehydration, thirst is a good indicator of when you need to swig. Here’s the deal: As water levels in the body drop, the blood gets thicker. When the concentration of solids in the blood rises by 2 percent, the thirst mechanism is triggered. A 1 percent rise in blood solids could be called “mild dehydration,” but it could also be considered a normal fluctuation in bodily fluids.

Either way, feeling thirsty is a good indicator that you need to get some water into your body, and soon. Serious symptoms of dehydration don’t arise until blood solids rise by 5 percent — long after you feel thirsty. But, obviously, you don’t want to wait that long. Even mild, subclinical levels of dehydration come with sacrifices in optimal vitality, metabolism and appearance. Like an underwatered plant, the body can survive on less water than it wants, but it’s unlikely to thrive.

It’s important to recognize, though, that drinking too much of the wrong thing can pose its own problems. Americans now drink nearly 21 percent of their daily calories, and those who glug down the most sugar-laden beverages are more likely to be overweight and obese than those who drink the least.

In a study published last year in the Journal of the American Dietetic Association, researchers found that people drank in response to thirst only 2 percent of the time. Obviously, a lot of the drinking we do, we do for pleasure or entertainment, not hydration.

“It’s easy to drink without thirst,” says Richard Mattes, PhD, MPH, RD, a professor of foods and nutrition at Purdue University in West Lafayette, Ind., and one of the study’s authors. “There is a large array of palatable beverages available to us much of the time and only weak internal signals inhibiting drinking. This facilitates drinking whether we’re thirsty or not.”

Bottom Line: Drinking water only when you’re thirsty may relegate you to being less than optimally hydrated much of the time, and it may undermine your energy and vitality. On the other hand, constantly sipping or gulping calorie- or chemical-laden beverages for entertainment is a bad idea. So if you tend to keep a bottle of soda on your desk all day, or if you’re never seen without your coffee cup in hand, rethink your approach. Get in the habit of drinking a glass of water first thing in the morning, and a few more glasses of water throughout the day. You may want to keep a glass or bottle of water nearby so you are prompted to notice thirst when it arises, or better yet, to drink proactively (especially important during strenuous exercise, long airplane flights and in hot weather).

Myth No. 5: Hydrating is all about water.

Reality: Nope. It takes a delicate balance of minerals, electrolytes and essential fatty acids to get and keep water where it needs to be — properly hydrating your bloodstream, your tissues and your cells.

“You can drink lots of water and still be dehydrated on a cellular level,” says Haas. Water you drink is absorbed from the digestive tract into the bloodstream by small blood vessels (capillaries). Of the water contained in food and beverages, 95 percent ends up in the blood. From the blood, water moves into the fluid surrounding the cells, called extracellular fluid. That’s important, but it’s not the end of the line. Water needs to get inside cells for you to maintain optimal health.

A person’s vitality is affected by how well his or her body gets water into and out of cells, says Haas. A variety of unhealthy lifestyle habits and health conditions can inhibit this cellular capacity, he notes. But naturally, too, as the body ages, the water inside cells (intracellular) tends to diminish, and water outside cells (extracellular or interstitial fluid) tends to accumulate. Haas calls this gradual drying out of cells a “biomarker of aging.”

Minerals, especially electrolytes and trace minerals, are essential to maintaining cellular equilibrium. Minerals help transport water into the cells, where they also activate enzymes. And enzymes are the basis of every biological process in the body, from digestion to hormone secretion to cognition. Without minerals, says Haas, enzymes get sluggish and the body suffers.

Without essential fatty acids — which form the basis for cellular membranes — cells can’t properly absorb, hold and stabilize the water and other nutrients they’re supposed to contain.

Bottom Line:Take in plenty of minerals by eating lots of fresh fruits, vegetables, nuts and seeds — ideally from produce grown according to biodynamic farming practices, meaning the farmer is supporting (rather than depleting) nutrients in the soil. Another way to boost minerals in the diet is cooking with a high-quality sea salt. A natural, unrefined sea salt will deliver up to 60 trace minerals your body needs to manage water flow. Also, try to include whole foods that are high in essential fatty acids, which are critical to maintaining healthy cell membranes that can hold in moisture. And consider a multimineral supplement that includes an ample supply of trace minerals in its formulation.