WATER

WATER

BODY COMPOSITION: Water is the major component of our body. If you weigh 50 kg, 31kg of that weight is water.

Approximately 55 to 70 per cent of the total body weight is made up of water. The percentage of water tends to decrease as a person gets older. Thus infants and children have a much higher content of water than adults. Fat individuals have less water than lean ones. Water is an essential nutrient next only in importance to oxygen. Deprivation of water even for a few days can lead to death.

Water is an essential component of every cell of our body. There is a variation in the water content of various tissues. Metabolically active tissues such as brain, liver, blood and muscles contain more water than bone and fat tissue, which are less active. For example, blood plasma has 90 per cent, muscle tissue 75 – 80 per cent and fat tissue 20 per cent water.  Water holds innumerable body components in solution or suspension.  Therefore, it is more appropriate to refer to these as fluids. The fluids, which exist inside the cells, are called intracellular fluids, which form about 55 per cent of water in the body. The rest is found as extracellular fluid (outside the cells). Blood, lymph circulation and interstitial fluid (fluid between cells or tissues) are part of extracellular fluid.

The fluid balance is maintained between the compartments as also between blood and interstitial fluid, kidneys are the final regulators of fluid balance.

FUNCTIONS: Water serves as a building material for each cell of the body.

Water is a universal solvent and is able to dissolve all the products of digestion. Further as it is a constituent of all body fluids, it helps in the transport of the products of digestion to the appropriate organs. For example, blood, which contains 90 per cent water, carries carbon dioxide to the lungs, nutrients to the cells and waste nitrogenous material and salt to the kidneys. Urine which contains 97 per cent water has all the waste material dissolved in it and the body is thus able to excrete soluble waste products of metabolism. Water is needed for many chemical reactions to occur in the body. For example, the breakdown of sugar to simpler substances needs the presence of water. Water acts as a lubricant preventing friction between moving parts of the body. The body temperature is regulated through the evaporation of water from the skin and lungs.

Table: Water Balance in a Healthy Adult.

Water intake	Water loss
Water intake--- 800 to 1100 ml	Urine--- 800 to 1000 ml
Water in food --- 600 to 900 ml	Vapor ---600 to 1000ml (skin and lungs)
Metabolic water --- 200 ml	Faces ---- 200 ml
Total:                      2200 ml	1600 ml to 2200 ml

NORMAL LOSSES: Kidneys and lungs carry out water from the body. Water is also lost as perspiration through the skin and as part of excreta from the bowel. The volume of urine voided depends on the intake of fluids and varies from 400 to 1400 ml.

The minimum or obligatory excretion of urine is about 600 ml to keep all the solutes (salt, urea, etc.) to be excreted in solution. Water is lost as vapor through the skin (insensible perspiration) and also as visible perspiration in hot weather and after strenuous.

WATER BALANCE: The body normally maintains a water balance preciously, i.e., the amount of water ingested is equal to the water excreted or lost from the body. This water balance is maintained even though the fluid intake may vary widely from day- to- day. How exactly this regulatory mechanism works is not known, but certain regions of the hypothalamus are believed to regulate the intake.  The water excretion is controlled by the hormones.