Illustration of a capacitive deionisation cell works. Capacitive deionisation is a process in which ions such as salts (blue and green) are removed from brackish water by the application of an electric field. When the power is on, electrons (black with white minus symbol) flow to the upper electrode, making it negatively charged and leaving positive holes in the lower electrode. The electrodes (dark grey) attract the opposite charged ions in the water and absorb them into a porous surface, leaving the water free of salts. The system also stores the electric charge (capacitance) like a battery. When the power is off, electrons flow back to the electrode they came from, and the flow can be used to power electrical components. For a version of this image with labels, see C060/2163.