All in one” unit in a cabinet housing with lockable door and viewing window. All components (pretreatment, softening, reverse osmosis, electro-deionization, pure water tank with level control and pressure increase) are integrated and pre-assembled ready for connection. Multilingual microprocessor control with LCD display for controlling and monitoring pure water systems. Display of the permeate and pure water conductivity, fully automatic rinsing cycles and potential-free fault messages. Subsequent modular capacity increase possible.