Water is the simplest of all the nutrients, yet it is the most important. Without it, life could not exist. Life probably began in water billions of years ago, and it is still essential at every stage of growth and development. Water brings to each living cell the ingredients that it requires and carries away the end products of its life-sustaining reactions. The life functions of assimilating, digesting, absorbing, transporting, metabolizing, and excreting nutrients and their by-products all rely on water. The body’s cells are filled with water and bathed in it. The human body averages 55 to 60 percent water, and losing as little as 10 percent of it can result in death. Water balance is maintained by drinking fluids and by eating foods, all of which naturally contain at least some water. A small portion is also obtained through metabolic processes.
People get the water they need from foods and beverages. Although it may not always be apparent, many foods contain more water than any other nutrient. Foods range in water content from 0 to 95+ percent. Those that yield the most water are fruits and vegetables, ranging from 70 to 95 percent. Whole milk, which is over 80 percent water, and most meats, which average just under 70 percent water, are also high in water content. The foods with the least water include vegetable oils and dried foods such as grains and beans.
The water in food may be either “free” or “bound” form. Free water, the largest amount of water present in foods, is easily separated from the food, while bound water is incorporated into the chemical structure of other nutrients such as carbohydrates, fats, and proteins. Bound water is not easily removed and is resistant to freezing or drying. It also is not readily available to act as a medium for dissolving salts acids or sugar.