On average, male bodies have about 60% water, whereas female bodies, due to more fatty tissue, have about 55%. Newborns are about 75-80% water, reducing to 60-65% within the first year after birth.

Body and water composition varies between genders and fitness. The more fatty tissue, the less amount of water. Mental concentration and physical coordination can decrease at a loss of even 1% water concentration in the human body. The involuntary thirst sensation does not start until the water concentration drops 2-3%. Dehydration can begin to be classified as mild to severe when the percentage drops 5%.

Water has many functions in the human physiology. Among them are: Used to construct new cells; assist to metabolize proteins and other nutrients; and as an insulator from both heat and physical impacts (shock).

There are many recommendations on the amount of water a person should drink in a single day, ranging from 2 liters all the way to 4 liters.

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