Demineralisation Plants, DM Plants. Demineralisation is the process of removing mineral salts from water by using the ion exchange process. With most natural water sources it is possible to use Demineralisation and produce water of a higher quality than conventional distillationDemineralization is the process of removing mineral salts from Water by using the ion exchange process. Demineralised Water is Water completely free ( or almost ) of dissolved minerals as a result of one of the following processes : Distillation. Deionization.