Water

About 65% of our body is water, so water is essential for our health and well-being. Water serves as a solvent for most bodily components being the fluid in which almost all biologic processes take place.

Normally about 20% of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included).

Water is lost from the body through urine and feces, through sweating, and by evaporation. With physical exertion and heat exposure, water loss and daily fluid needs increase.

Sources

Drinking water comes from surface water and ground water. Water suppliers use a variety of treatment processes to remove contaminants and impurities including microorganisms.

The most commonly used processes include filtration, flocculation and sedimentation, and disinfection. In some cases ion exchange and adsorption have to be applied.

Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes.

Daily intake

We need at least 6–8 glasses of water daily to maintain proper hydration. However, the latest dietary reference intake report by the United States National Research Council recommended 3.7 liters for men and 2.7 liters for women. Pregnant and breastfeeding women need additional fluid to stay hydrated.

The Institute of Medicine (U.S.) recommends that, on average, men consume 3.0 liters and women 2.2 liters. Pregnant women should increase intake to 2.4 liters and breastfeeding women should get 3 liters, since an especially large amount of fluid is lost during nursing.

In warm weather and while exercising you need to drink more water to replace the increased loss due to sweating and evaporation. If you drink too little in those circumstances you can develop dangerous dehydration.

Even if elderly people have a lower energy consumption, they should not decrease their daily volume of water, because the renal concentrating capacity decreases with age.

Deficiency

Deficiency of water (dehydration) can occur in warm weather and while exercising because of an increased loss of water due to sweating and evaporation.

Symptoms may include headaches, decreased blood pressure (hypotension), and dizziness or fainting when standing up. In advanced cases delirium, unconsciousness and, in extreme cases, death can occur.

Excess

If your kidney function is reduced, you can develop overhydration - even water intoxication - if you drink far more water than necessary. Water intoxication is a serious and potentially fatal condition. If the kidney function is normal, it is difficult to drink too much water.

References: 1 , 2 , 3