The definition of a water coil is a type of heat exchanger that is used to transfer heat from one medium to another. It is most commonly used in heating and cooling systems, such as those found in buildings, to transfer heat from a heated fluid such as hot water, steam, or refrigerant to a cooler fluid such as air or water. A water coil consists of a series of copper or aluminum tubes that are bent into a coil, with a series of fins attached to the outside of the tubes. These fins increase the surface area of the coil, allowing it to transfer more heat. Generally, the water will enter the coil and travel through the tubes, while air is circulated around the fins, which then transfers the heat from the water to the air. The water then exits the coil and is returned to the heat source. This type of heat exchanger is highly efficient and can be used to provide both space heating and cooling. It is also used in industrial processes, such as