Cooling water can be from any source, but the following basic requirements are needed:

　　1. Water should be clean.

　　2. Water temperature should be between 5 and 30°C.

　　3. The pressure delta between the inlet and outlet should be 207-275kPa.

　　4. The flow rate specified for the equipment must be available at all times.

　　Because the quantity of water required is too expensive to draw from a city water system and dump down the sewer without recirculation (and possibly illegal), most customers select external cooling systems, sold and installed by other suppliers, that re-circulate the water. This is especially beneficial when more than one system is involved, as one cooler can handle multiple systems. There are two types of coolers:

　　Evaporative coolers (Cooling Towers) which use the evaporation of a water spray to cool the re-circulating water. This method still consumes some water via the evaporation and cannot cool to lower temperature.

　　Chilled coolers, which use a refrigeration system to cool the water. This system then uses an air cooled condenser to expel the heat outdoors.

　　Either system may use ethylene glycol (anti-freeze) mixed with the water to extend the temperature range of the cooling loop, mostly to avoid freezing. The use of anti-freeze makes the cooling less efficient, which means a higher overall flow rate is required.