NOVELTY - Apparatus for generating electricity from water (11), comprises first and second master electrodes (where the electrodes define a flow path allowing water to flow along the electrodes, and the apparatus is constructed to alternately allow water with a relatively high ion concentration and water with a relatively low ion concentration to flow along the electrodes thus charging or discharging the electrodes generating electricity), and a floating electrode (5) located between the first and second master electrodes in the flow path.    USE - The apparatus is useful for generating electricity from water.    ADVANTAGE - The apparatus generates electricity from water with an improved efficiency, and adds up the voltage differences over each floating and master electrodes, and thus the voltage output is sufficiently high to avoid significant losses in the power converter.    DETAILED DESCRIPTION - Apparatus for generating electricity from water (11), comprises first and second master electrodes (where the electrodes define a flow path allowing water to flow along the electrodes, and the apparatus is constructed to alternately allow water with a relatively high ion concentration and water with a relatively low ion concentration to flow along the electrodes thus charging or discharging the electrodes generating electricity), and a floating electrode (5) located between the first and second master electrodes in the flow path, where at least one of the master and floating electrodes is provided with a selective ion barrier layer which is selectively impermeable for either anions or cations so that in use cations or anions of the water with the relatively high ion concentration will flow through the selective ion barrier layer thus charging the electrodes. An INDEPENDENT CLAIM is also included for generating electricity comprising: providing at least two master electrodes and at least one floating electrode located between the master electrodes, where at least one of the master and floating electrodes is provided with the selective ion barrier layer; and alternating a flow of water with a relatively high ion concentration with a flow of water with a relatively low ion concentration along the electrodes, thus allowing anions or cations of the water with the relatively high ion concentration to flow through the selective ion barrier layer for charging the electrodes and creating an electrical potential difference between the two master electrodes from which electricity is generated.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of reverse capacitive deionization system.    Anode master electrode (1)    Current collector (2)    Cathode master electrode (3)    Floating electrodes (5)    Water (11)