Water is the most abundant substance in the body. Its abundance is due partly to its unique chemical properties created by the influence of its hydrogen bonds. These properties include the following:
- Solvency. Water is an excellent solvent. Ionic substances are soluble in water (they dissolve) because the poles of the polar water molecules pull them apart, forming ions. Polar covalent substances are also water‐soluble because they share the same hydrogen bonding as water shares with itself. For this reason, polar covalent substances are called hydrophilic (water loving). Because they lack charged poles, nonpolar covalent substances do not dissolve in water and are called hydrophobic (water fearing).
- Cohesion. Because water molecules are held together by hydrogen bonds, water molecules have a high degree of cohesion, or the ability to stick together. As a result, water has strong surface tension. This tension, in turn, gives water strong capillary action, allowing water to creep up narrow tubing. These qualities contribute to the movement of water through capillaries.
- Stability. The temperature of water is stable. You must add a relatively large amount of energy to warm (and boil) it and remove a large amount of energy to cool (and freeze) it. So, when sweat evaporates from your forehead, a large amount of heat is taken with it and you are cooled.