EMERALD – electrochemical devices to remove from fresh water all species and forms of microorganisms, heavy metal ions and harmful organic compounds. A source solution for these devices is fresh water proper. Mineralization of purified water is only slightly different from that of initial water since the contribution of heavy metal ions into the general specific electric conductivity of water is negligible. The technology of purification consists in a definite order of stages of water treatment in active and passive elements (reactors). The active elements of water purification flow chart are RPE flow-through electrochemical modular reactors made up of combined or single FEM-3 modules, in which purposeful non-equilibrium alteration of water physical and chemical parameters and properties occur, that is, its inner energy rises. This is accompanied by electrochemical transformation of inorganic salts dissolved in water not exceeding 10 % of their total content. The passive elements are catalytic, flotation, electrokinetic reactors and those for micro-electrophysical water conditioning. In these passive elements excessive internal water energy is selectively used for purification processes. Depending on water characteristics and the nature of impurities various purification methods are employed, which differ by the sequence of water treatment stages, their type, quantity and intensity.