Minerals in natural water can destroy desirable coolant properties. Additionally, organic contaminants in such water can accelerate bacterial growth. Eventually, after repeated usage, coolants become unusable because the inhibitors, stabilizers, wetting agents and other functional additives lose effectiveness. Remember that used coolant may not be dumped down sewers, poured into surface waters or dumped on land. Coolants that are essentially oils, such as mineral oil, can be re-refined or blended with other oils.
Oil refiners are available to provide such services.
The separation is most often done chemically by adding an acid or salt. Normally, the water can be drawn off with sufficient purity to be capable of discharge into municipal sewage treatment facilities. The oil fraction, however, must be handled as a waste oil.