Water is a unique molecule with basic properties that make it ideal for cooling water applications. For example, it is safe, easy to handle, widely available, and inexpensive in most industrialized regions of the world. Water is a more efficient heat transfer medium than many other materials, especially compared to air. Water cooling is a method of heat removal from components and industrial equipment. As opposed to air cooling, water is used as the heat conductor. Water cooling is commonly used for cooling automobile internal combustion engines and large industrial facilities such as steam electric power plants, petroleum refineries, hydroelectric generators and chemical plants. Other uses include cooling of lubricant oil in pumps, cooling the barrels of machine guns; for cooling purposes in heat exchangers; and recently, cooling of various major components inside high-end personal computers. Recent trends in cooling water systems and modern approach in use of corrosion inhibitors for cooling water systems are presented. This book is useful to those working on corrosion inhibitors, mainly to those working on corrosion inhibitors for cooling water systems.