Nothing refreshes like an ice-cold glass of water on a hot summer day.
Water replenishes the body's cooling system, enabling it to survive sweltering heat or elevated body temperatures due to exercise. Sweating cools the body by evaporating water on the surface of the skin and dispersing excess heat.
But until the tap runs dry, most people take water for granted. Recent contamination of municipal water systems in the Midwest due to flooding, as well as a disease-borne outbreak in Milwaukee last (month), devastated millions of people.
Although deficiencies of other nutrients can be sustained for months or even years, a person can survive only a few days without water. Indeed, experts rank water second only to oxygen as essential for life.
In addition to offering true refreshment for the thirsty, water plays a vital role in all bodily processes. It supplies the universal medium in which various chemical changes of the body occur, aiding in digestion, absorption, circulation and lubrication of body joints.
For example, as a major component of blood, water helps deliver nutrients to body cells and removes waste to the kidneys for excretion. Enzymes essential to digestion are also primarily water, working to break down food so that nutrients can be absorbed in the intestine.
Water comprises about 50 to 70 percent of body weight in humans. Males on average have a higher percentage of body water than females, because they tend to have less body fat. The more body fat in individuals, the less water therein. A decrease of as little as 10 percent of adult body water due to excessive vomiting or diarrhea is considered serious, and in a young child, could be fatal.
Average adults need about 64 ounces (eight cups) of fluid each day for optimal health. Although experts generally advise drinking several glasses of water a day, the need for fluid can also be met by consuming a variety of foods and beverages.
Milk is about 87 percent water; meat ranges from 40 to 75 percent water; and vegetables are as much as 95 percent water. Even foods normally considered "dry" such as cereal and bread contain about eight to 35 percent water.
Water supplies small amounts of many minerals vital for life, such as sodium, potassium, calcium, copper and magnesium. Minerals such as calcium are essential to bone formation and blood clotting, while magnesium is needed to produce energy and conduct nerve impulses. Different concentrations of these minerals determine whether water is considered hard or soft.
Hard water contains high concentrations of calcium and magnesium and is often associated with residues or crystals in the teapot over time. The principal mineral of soft water, on the other hand, is sodium. Soft water dissolves soap better, leaving fewer mineral deposits, and is therefore often viewed as more desirable.
But it's been suggested that sodium in soft water contributes to increased incidence of high blood pressure and heart disease in some populations. According to Jennifer Orme-Zaveleta, chief of the Environmental Protection Agency's (EPA) drinking water health assessment section, "Drinking water is not a significant source of sodium in the diet. You get much more sodium from salty foods, even in areas with a relatively high sodium concentration in the water, than from water itself"