Water Intake And Fluid Balance

A regular fluid intake from our daily diet is crucial to maintain good health. This is because the human body does not store water in the way it stores calories (as glycogen or body fat), so we need a constant supply every day. The human body loses on average the equivalent of 6-12 cups of water each day, in the following ways:

– 28-40 ounces of water are lost in breath and perspiration.
– 20-55 ounces are lost during urination.
– 2-7 ounces are lost via the gastrointestinal tract (feces).

About 15 percent of our water needs comes from food metabolism, as our body converts part of our food into hydrogen and then mixes this with oxygen from our lungs to form water. The remaining 85 percent comes directly from water in our diet, either from water-rich foods or from water we drink.

A Healthy Water Intake

For women, the US Food and Nutrition Board recommends a total daily water intake of about 2.7 liters (about 8 glasses) from all beverages and foods. For men they advise a total daily water intake of about 3.7 liters (about 12 glasses).

How The Human Body Uses Water

The most important characteristic of water is that it’s a solvent – meaning, it dissolves other substances. So it carries nutrients and other important chemical material around the body, allowing all organs to perform their functions in order to maintain good health. For example, water helps to digest food, dissolving nutrients to enable them to pass through the gastrointestinal walls into the bloodstream. It also helps food to pass through the small and large intestines. Water in the lymphatic system (link) helps to remove waste products from the body. In addition it provides a medium within which electrical messages can be transmitted between cells and around the body, permitting (eg) the muscles, eyes and brain to operate. Water also allows biochemical reactions to occur, such as metabolism. As well as this, water helps to lubricate the organs and tissues, acts as a shock absorber for the spinal cord and eyes, and regulates temperature by cooling the body with moisture (perspiration) which evaporates on the skin. Thirst, the principal symptom of fluid loss or water depletion, is influenced by a group of nerve cells in the hypothalamus located at the base of the brain.

Water Is Found In All Body Fluids

Water is located throughout the body. It’s actual distribution is determined by osmotic and hydrostatic pressures. Roughly 75 percent is inside the cells (intracellular fluid), while about 25 percent is outside the cells (extracellular fluid). The latter includes: (1) interstitial fluid (aka tissue fluid, or intercellular fluid) the fluid which bathes and surrounds the cells. (2) Blood plasma, the clear liquid found in blood. (3) Lymph, the yellowish fluid which is extracted from body tissue by the lymphatic system (a complex network of lymphoid organs, lymph nodes, ducts and capillaries and lymph vessels) and then directed back into the blood vessels of the circulatory system. Water is also found in body fluids like sweat, seminal fluid and vaginal fluids.

How The Body Maintains The Correct Fluid Balance Inside Its Cells

Not only do we need to maintain a healthy water intake, in addition we need to maintain a healthy fluid balance inside and outside our cells. For example, although cells that contain too little water will die, those that contain too much will rupture and burst. The human body maintains a proper fluid balance through the action of mineral compounds (mostly from sodium and potassium) called electrolytes in conjunction with the sodium pump. Put simply, the sodium pump is a mechanism which ensures that a cell does not retain too much sodium (which attracts water via osmosis across the semi-permeable membrane of the cell wall) and thus stops too much water from entering the cell.