Air separation equipment generally uses rivers, lakes or groundwater as cooling water. This kind of water usually contains suspended solids (sand and other dirt) and bicarbonates such as calcium and magnesium [-Ca(HCO3)2 and Mg(HCO3)2], which is called hard water. When there is a lot of suspended matter, it is easy to block the channels, filters and valves of the cooler. When the water temperature rises, bicarbonates such as calcium and magnesium easily form calcium carbonate (CaCO3) and magnesium carbonate (MgCO3) precipitates, which form the so-called scale. Generally, water scale will begin to form when the water temperature is above 45℃, and the higher the water temperature, the easier it is to scale. The scale adheres to the pipe wall of the cooler, the filler of the nitrogen water pre-cooler, the nozzle or the screen hole, etc., which not only affects the heat exchange and reduces the cooling effect, but also hinders the circulation of cooling water or air, which may cause equipment failure in severe cases. For example, the nitrogen water pre-cooler carries water, which makes the cold storage (or switching heat exchanger) freeze. The scale is relatively hard and difficult to remove when attached to the wall of the vessel. Therefore, the cooling water is preferably softened. It is relatively simple to use a magnetic water device for softening treatment, and the effect is acceptable. A sedimentation tank should be installed to remove suspended solids. If the cooling water is recycled, it will help soften the water quality, but it occupies a large area and requires a large investment in infrastructure.

　　For the compressor cooling water, the temperature is generally not higher than 28℃, and the discharge temperature is lower than 40℃. The water quality requirements are:

　　pH value 6.5～8.0

　　Suspended matter content is not more than 50mg/L

　　Temporary hardness is not more than 17°dH

　　Oil content is less than 5mg/L

　　Chloride ion (C1-) (mass fraction) less than 50×10-6

　　Sulfate (SO4-2) (mass fraction) less than 50×10-6

　　The water supply and drainage of the nitrogen water pre-cooling system is an independent circulation system. Because the cooling water in the tower has a large temperature rise, high drainage temperature, and serious scaling, the system is required to use low-hardness or soft water as much as possible for the supplementary water of the system. Its temporary hardness should generally not be greater than 8.5°dH. Other requirements are related to compressors. The cooling water is the same.

　　The lubricating water of the cylinder of the high-pressure oxygen compressor for bottle filling should be distilled water or soft water.