Water is essential for life. Approximately two thirds of the body is water and two thirds of the earth is covered by water. H2O is a polar molecule that has many important biological characteristics. Water has high heat capacity, it absorbs and releases large amounts of heat before changing temperature itself. As part of blood, water redistributes heat among body tissues, ensuring temperature homeostasis. Water has high heat of vaporization. When water evaporates, it changes from liquid to gas. Water in perspiration helps cool the body. Water has polar solvent properties. Because water molecules are polar, they orient themselves with their slightly negative ends toward the positive ends of the solutes in a water solution and surround them. The polarity of water helps ionic compounds, acids and bases dissociate in solution and become evenly scattered in the solution. Water is the body’s major transport medium. Nutrients, respiratory gases, and metabolic wastes carried throughout the body are dissolved in blood plasma, and many metabolic wastes are excreted from the body in urine. Mucus is another fluid lubricant in the body that is made up of water. Water is a reactant in many chemical reactions in the body. Hydrolysis reactions add water to the decomposition reactions in the body to break the chemical bonds of the nutrients that are eaten to break them down into smaller molecules that can be carried across the intestinal wall for example. Conversely, when large carbohydrate or protein molecules are synthesized from smaller molecules, a water molecule is removed for every bond that is formed. Water is a cushion that helps protect from physical trauma. The cerebrospinal fluid that bathes the brain is an example of waters cushioning ability. Without the correct amount of water in the system the animal will become dehydrated and body temperature will rise to cell damaging temperature levels, proteins will start to unravel and enzymes will not work when their shape is changed by the excess heat. In the next blog we will talk about the different pathological conditions that are caused by dehydration and how to make sure your animal companion gets a sufficient amount of quality water into their system.