Mixed bed demineraliser plant embodies a single column of Cation and Anion resin material mixed intimately together. Water passing through the column comes repeatedly in contact with these resins and is thus is effect subjected to an almost infinite number of demineralising stages. Demineralised water of extreme purity is produced-purity that can not be equaled by any other commercial method. Mixed bed demineralizers are regenerated with acid and alkali but the ion exchange resins must be separated and superimposed layers are thus formed into which the acid and alkali solutions and rinse water are introduced through specially designed spreaders. After regeneration the two resins are remixed with compressed air.