The Fundamentals of H2O

Water is essential to life; in fact, human beings are essentially big sacks of water. Water accounts for 60–95 percent of our living cells, and 55 percent of the water in the human body is in intracellular fluids. The remaining 45 percent (extracellular) is divided between the following:

• Plasma (8 percent)
• Interstitial and lymph (22 percent)
• Connective tissue, cartilage, and bone (15 percent) Water also is necessary as a solvent for the multitude of biochemical reactions that occur in the body:
• Water acts as a transport medium across membranes, carrying substances into and out of cells.
• Water helps maintain the temperature of the body.
• Water acts as a solvent (carrying dissolved chemicals) in the digestive and waste excretion systems.

Healthy humans have an intake/loss of about two liters of water per day. The intake is about 45 percent from liquids and 40 percent from food, with the remainder coming from the oxidation of food. The loss is about 50 percent from urine and 5 percent from feces, with the remainder leaving through evaporation from the skin and lungs. A water balance must be maintained within the body. If the loss of water significantly exceeds the intake, the body experiences dehydration. If the water loss is significantly less than the intake, water builds up in the body and causes edema (fluid retention in tissues).