Torch coolant is a mixture of de-ionized water and ethylene or propylene glycol to depress the freezing point. Many shops use plain de-ionized water if there is no risk of freezing. De-ionized water must be used because it is free of conductive ions that can cause problems in the system. Ethylene or propylene glycol is the same agent used in automotive cooling systems. However automotive antifreeze should never be used in a plasma system! Most commercial antifreeze has material in it to clog small leaks. This makes it unsuitable for use in a plasma torch