EPA Office of Ground Water & Drinking Water

Over half of your body is made up of water. It's in every cell and every tissue. Biological processes like circulation, digestion, absorption and excretion depend on water. It forms the foundation of blood and lymph, maintains hearty muscles and young-looking skin, lubricates joints and organs and regulates body temperature. You can't function without it.

The average human brain weighs about three pounds and all but ten ounces is water.

One talks of rainwater, seawater, bath water, drinking water, waste water etc. Even humans are made up of mostly water, men of 60 % and women of 50 %. A human cell consists of 73 % water.

Different types of water are called different names on the basis of the properties of the water. All these different names for water are a generally adopted concept. However, all types of water contain the "same" molecule. Its chemical formula is H₂O – a chemical compound of hydrogen and oxygen (dihydrogen oxide).

Water is by far the best solvent. This is a big advantage but also a drawback, since almost any other substance can be dissolved in water. That is why water is so easily contaminated.

Besides pure water (water molecules) there are a great number of different substances and chemicals, which change and add different properties, characteristics and names to the water. Its amazing how little of another substance that is needed to totally change the properties of water.