A water chiller is an industrial water refrigeration apparatus that produces cold water to cool industrial process equipment. A water chiller is a complete system filled with refrigeration equipment, including a condenser, refrigerant, pipes, coolant expansion reservoir, pumps, and so on. Water is cooled to temperatures around 20°C (68°F) and pumped through a hydraulic circuit to reach the process equipment.

Industrial chillers can circulate as much as 400 tons of water. These units start at around US$2,500 and go up from there. Because some water chillers can be bulky, they are often designed to be stored on the side or roof of an industrial building and controlled from the inside.

Water chillers are a popular alternative for industrial facilities growing fast enough that the move from city water to specialized chilling units becomes cost-effective. Water chillers are also a well-known alternative to evaporative cooling towers. They are often claimed to be superior to towers in that the coolant water comes into contact with air in a tower, but stays in a closed circuit in a water chiller system.

Selecting a water chiller requires calculating the exact amount of chilling needed, that is, the precise amount of energy added to the coolant by the process machinery. Then a water chiller may be selected for maximum efficiency.

Water chillers conserve water by cycling the coolant in a closed circuit, rather than continuously pumping in city water. Adequate cooling is especially necessary in precision manufacturing, where slight overheating can cause thousands of dollars in lost product or equipment. Some specialized chillers can lower the temperature of non-water coolants to as low as -50°C (-58°F). Process equipment that requires cooling includes lasers, ozone generators, plastic applications, vacuum pumps, cutting and welding machines, packing and printing machines, X-ray machines, STM microscopes, and plenty more. Smaller water chillers are used around the home to produce tasty drinking water, or to cool water for use in aquariums.