Abstract: A device for treating water having a cartridge, which includes a container for receiving treatment means and a connecting head. Furthermore, a connecting device is provided, which is equipped with a holder, a valve device, and a locking device. The holder has at least one side wall, on which the inflow and outflow openings are disposed. The valve device has a valve element, which surrounds the connecting head at least partially and is disposed movably in the holder. The associated cartridge provides at least one inlet opening and at least one outlet opening on at least one side surface. The cartridge has at least one recess and/or a lug for the engagement of a locking element of a locking device of the connecting device.