There is a significant amount of research showing the detrimental effects of chronic, mild dehydration. Our favorite book on this subject is Your Body’s Many Cries for Water, by Dr. F. Batmanghelidj, M.D. This book is a must read for everyone interested in improving their health.
(The websites of many companies offering water filtration products borrow heavily from the book above without giving proper credit to the author.)
Proper hydration is absolutely essential to wellness and vitality, as well as proper function of nearly every bodily process. Chronic dehydration, however mild, pushes your internal environment towards one where disease conditions flourish. Once you have made the decision to increase your water intake, you will want to know how much water you really need...
Every day we lose water through sweating (noticeable and unnoticeable), exhaling, and urinating. For your body to function properly, you need to replace this water by consuming beverages and foods that contain water. Room temperature or moderately chilled water is the best fluid to satisfy thirst and the most effective to replace fluid lost through exercise and perspiration. Unfortunately, our thrist impulse lags behind the body’s needs, so you should not wait until you are really thirsty to reach for a glass of water.
A healthy adult's daily fluid intake can vary widely. Most people drink fluid to quench thirst, to supply perceived water needs, and "out of habit." Because we feel thirsty a little after we need more water, there's considerable benefit from starting each day with a couple large glasses of water (totalling 16 oz or more.) This will typically provide about a ¼ of your daily needs, and help you start the day on a healthy note. Drinking water first thing in the morning will also reduce your appitite. We suggest you drink this water at least a half hour before eating, which will provide some time for the water to leave your stomach, and won’t dilute the stomach acids too much – which can impact how well enzymes in your stomach digest your food.
The International Sports Medicine Institute recommends 1/2 to 2/3 ounce of water per pound of body weight per day, ingested periodically throughout the day. Figured in liters, that's about three to four liters per day for the average-sized person. The calculation goes like this: divide your body weight (lbs) by two. That's the number of ounces of water you should consume each day.
If you’re a 200 lb man, you should drink 100 oz of water per day, or just about 3 liters, or just over 3 quarts.
If you are a 130 lb woman, you should be drinking about 65 oz of water per day, or roughly 2 liters (or 2 quarts).
Of course, in both examples above, if you exercise heavily, you will probably need much more water to overcome the fluid lost in respiration and sweat.
Thirst is not a reliable gauge for your fluid needs, especially as you grow older, because the body's thirst mechanism becomes less attuned. Interestingly, adults more easily confuse the sensations of hunger and thirst than children.
Anything that increases visible sweat loss or invisible sweat loss will increase overall water needs. Wind increases invisible sweat loss and therefore water needs increase if you are outside during windy times.
If a person doesn't drink enough water to balance the increased water needs, the kidneys produce a more concentrated urine which increases the risk of forming kidney stones. New joggers sometimes develop kidney stones because they don't realize how much more liquid they need to consume. It is very common to lose one to two liters of water in sweat during one hour of moderate exercise. During more intense exercise, sweat loss is even greater.
When exercising, you should drink water aggressively. Compared to watching TV all day, one hour of exercise may demand approximately a 50 percent increase in the amount of water your body uses. Since the human body can only absorb so much water at one time, the rate of ingestion should be matched, as closely as possible, to the rate of absorption.
For years it has been understood the rate-of-absorption equals about 1/4 liter per 1/4 hour (or a liter an hour). Recent research indicates some of us can do better, absorbing as much as 1/4 liter in 10 minutes. That means, for maximum efficiency and well-being, drink about 1/4 liter of water every 10 to 15 minutes during periods of intense exercise. In some conditions you will lose water faster than you can replace it. In those conditions, rest breaks, during which fluid is consumed, become important.
It is also important to know that in periods of extreme exercise it is possible to drink too much water (or too much sports drinks)—in which case the body’s electrolyte balance can become compromised and lead to a dangerous and sometimes fatal condition resulting from a severe lack of salt in the blood (hyponatraemic encephalopathy).
An average person should probably be drinking between 400 ml and 800 ml in an hour in most forms of recreational and competitive exercise. People exercising gently in a mild environment would probably need less, and professional athletes competing in warm environments at higher intensities would probably need more. Drinks that are cool are absorbed more readily by the exercising body than warm drinks, and those containing sodium, such as sports drinks, are also more quickly absorbed.
Fruit juices contain too much sugar to meet your body's demands for fluid during exercise.
Soft drinks, in addition to caffeine, have excess sugar (10 teaspoons per 12-ounce serving) and additives (especially diet soda). Cutting your soda intake could be the healthiest change you make this year. There is also evidence to support significant behavior change in children who shift from soda to healthier choices. (We hear this regularly from people who invest in a PWS BEV system. Many have told us their children greatly reduced the amount of soda they’d been drinking and now prefer the water from the BEV system instead.)