Humans are 65% water!

The body needs water to regulate temperature, moisten tissues in the mouth, eyes, and nose, lubricate joints, protect organs, prevent constipation, reduce the burden on kidneys and liver by helping to flush out waste, and to dissolve nutrients as part of the digestive process.

Although a person can survive for several weeks without food, the body cannot survive longer than a few days without fluids. A loss of water equivalent to:

• 1% of body weight is enough to cause thirst and to impact the ability to concentrate;
• 4% loss of hydration results in dizziness and reduced muscle power;
• 6% loss of fluids causes the heart to race and sweating ceases;
• 7% loss of hydration results in collapse and subsequent death if fluids are not replaced.

Water Regulation

Water Intake

In a normal diet, fluid is gained via food as well as in drinks.  Along with water, most drinks such as tea, coffee, juices, and milk hydrate the body.  However, alcoholic drinks may not contribute to body fluids as alcohol is a diuretic, a substance that increases the output of urine by the body.  Caffeine, such as found in energy drinks, coffee, tea, and sodas, is also a diuretic.  Caffeine has also been shown to have an impact on overall hydration, but significant amounts (300+ mg) are typically necessary to exhibit negative effects on the body.

The amounts of water in different foods vary.

Water Loss

Fluid loss occurs in various ways throughout the body with urination being the primary method. While the elimination of the urine is periodic, the formation of urine constantly occurs. Urination not only removes excess water from the body but also rids the body of nitrogen-containing compounds and other wastes.  A “typical” urine output is approximately 1.5 liters daily.

Perspiration (sweating) also removes fluid from the body.  When body temperature rises, fluids are secreted through sweat glands to the surface of the skin.  This fluid then evaporates which has a cooling effect and reduces overall body temperature.  A typical loss of water through sweating is about 0.5 liters per day.  With hot weather, exercise, or physical activity, water loss can increase to 2 liters per hour.

Because urine output and sweating are conscious and measurable methods of fluid loss, they are called “sensible” losses.

The body can also exhibit fluid losses in what are termed “insensible losses.”  Insensible water loss is constantly occurring every minute of every day.  These losses are neither consciously felt nor measureable.  These include events such as breathing (our expelled breath contains moisture) and defecation (feces also contain water).

As can be seen by the above information, water intake and water loss should be balanced in order to prevent dehydration and to maintain a healthy body.