• human body is about 70 percent water. This water contains many types of solutes, including table salt. The amounts of these solutes in our bodies must remain constant day by day, and hour by hour. We have seen how regulating our internal body temperature is an important example of homeostasis.

Water is a molecule composed of two hydrogen atoms (H) and one of oxygen, so its chemical formula is H2O. This bond is so strong that for a long time it was believed that water was an element and not a compound.

regulate the chemical composition of body fluids by removing metabolic wastes and retaining the proper amounts of water, salts, and nutrients. Components of this system in vertebrates include the kidneys, liver, lungs, and skin.

• Water is a substance that works like a quick fluid in our body and helps us to eat well.