De-ionisation (or demineralisation) uses specially manufactured ion exchange resins which remove total dissolved solids and ionized minerals from water. As the majority of water impurities are dissolved salts, de-ionisation produces a high purity water that is generally similar to distilled water, and this process is quick and without the problems associated with scale build up. The system is useful for many commercial applications which require a higher water purity. It has a simple in/out head, and is a non-regenerating system, so resin is replaced as required.