Water comprises about 60% of our total body weight, and 72% of our brain. Even slight drops in fluid levels can significantly affect our health.

Over the years, the medical world has developed a general recommendation of drinking eight, 8-ounce glasses of water daily. This directive is a recommendation, with little or no research to support it.

The Institute of Medicine suggests men drink 3.7 liters and women 2.7 liters of water per day. This guideline is based on the concept of replacing the fluids we lose in a day. On average we excrete 1.5 liters of fluid as urine and another liter through breath, sweat, and bowel movements, for a total of approximately 2.5 liters. Assuming we absorb some fluid from the food we eat, 64 ounces of water simply replaces the fluid lost in a day.

Signs of dehydration

If you are drinking enough water, your urine will be clear and odor-free. If urine is very concentrated, e.g. dark yellow with a strong smell, you need to increase your fluid intake. B vitamins color the urine deep yellow, so if you are supplementing B vitamins, you can ignore the rule of thumb of having clear urine.

Other later stage signs of dehydration include

  • Headache
  • Dry mouth
  • Dry skin
  • Constipation
  • Mental fogginess
  • Dizziness/light-headedness
  • Muscle cramps
  • Nausea and vomiting
  • Shortness of breath
  • Fatigue
  • Fast heart rate (tachycardia)

You can test for “tenting” of the skin: pinch together the skin on the back of the hand. When you release the skin, it should quickly spring back to its normal shape. If the skin “tents,” you are very dehydrated. Many nursing homes commonly use this test to check residents for dehydration.

Pay special attention to infants and young children. They are unable to report symptoms, so you will need to be particularly attentive to signs of dehydration. In early stages of dehydration, a child may be fussy with a dry mouth and tongue. Another marker is the number of wet diapers you change (ideally 4 – 6 sopping wet diapers per day). In later stages of dehydration, the infant will be listless, possibly even unconscious, with rapid heart rate and shallow breathing. The fontanelle, or soft spot at the top of the skull, may be sunken.


Drinking small amounts of water frequently provides more sustained hydration in the body. If you drink lots of water in a short period of time, the kidneys will quickly dump much of the fluid. Aim to drink 8 – 12 ounces per hour, rather than a quart at one sitting.

How much water do I need?

Several factors influence how much water your particular body needs:

  • Body weight
  • Activity level
  • Climate
  • Altitude
  • Illness
  • Dietary factors

Body Weight

One rule of thumb for determining optimal fluid intake is to consume half your body weight in ounces of water. If you weigh 200 pounds, for example, ideally you would drink 100 ounces of water.

Activity Level

Physical activity, particularly during warm weather, causes more fluid excretion. The American College of Sports Medicine suggests drinking 17 ounces of fluid about two hours before exercising. Begin drinking fluids early during physical activity, and continue drinking at regular intervals (e.g. every 10 minutes) to replace fluids lost through breath and sweat.


The drier the climate you live in, the more water you will need to drink. Living in the high desert at 6,000 feet, I’m very aware of how the arid desert sky wicks moisture out of my body. If you live in a humid climate with little sun, you may need a bit less fluid.


High altitude environments also wick moisture out of the body. Although “high altitude” is defined as greater than 8200 feet, the body needs significantly more water even at lower elevations. At 6000 feet above sea level, for example, you perspire and exhale twice as much moisture as you do at sea level. You may need to increase water by one quart or more per day. The higher you climb (or live), the more water you will need.

Illness and physical conditions

Certain illnesses can increase your need for fluids. During an acute fever, for example, you will need to increase fluids to compensate for sweat and higher core body temperature. Remember water comprises 72% of the brain, so the brain and central nervous system are particularly susceptible to damage from a high fever. Usually during an illness appetite decreases, so less of your fluid intake will come from food. Increase water and diluted fruit juices during acute illnesses to restore fluid and electrolytes.

Women who are pregnant or breastfeeding need to increase fluid. According to the Institute of Medicine, pregnant women need 2.3 liters of fluid per day, and breastfeeding mother 3.1 liters of water. Modify these recommendations according to climate, elevation, and food intake. Breastfeeding mothers at higher altitude will need to increase fluids, as will mothers living in hotter climates.

Dietary factors

Fruits and vegetables can augment your fluid intake. Tomatoes and watermelon, for example, are almost 90% water.

Other foods and drinks, however, can detract from overall water intake. Alcohol acts as a diuretic, making you excrete more fluid than you ingest. Dehydration contributes to the classic “hangover” symptoms. Research varies on the effect of caffeine. If you do not regularly drink caffeinated beverages, an 8 ounce cup of coffee or caffeinated soda can cause you to excrete two or three times that amount, dehydrating the body instead of increasing overall fluid levels. Studies vary on the effects of caffeine for regular caffeinated beverage drinkers.

Increasing sodium intake causes the body to excrete more fluids by suppressing Antiduiretic Hormone (ADH).



The Bodies Many Cries for Water