Deionised water — the same product sold as demineralised water — is purified water from which dissolved mineral salts have been removed. It is produced by passing water through ion-exchange resins that swap calcium, magnesium, sodium, chloride, and other ions for hydrogen and hydroxyl ions, which combine into pure water; reverse osmosis often does the rough work first. What remains is water of very low conductivity, free of the hardness and dissolved solids that interfere with precise work. Food laboratories depend on it for preparing reagents, calibrating instruments, and running analyses where tap-water minerals would distort results. In manufacturing it feeds boilers, rinses equipment without leaving scale, and goes into products — from soft drinks to pharmaceuticals — where mineral content must be exactly controlled. It is chemically pure, but it is not sterile and not intended as drinking water.