Abstract: In a device for the treatment of water with a supply container for the provision of a regeneration agent solution and also with a piston-stroke controlled metering device for the allotting of feed-water into the supply container, wherein the exactly defined water volume which is displaced with one piston stroke can be supplied to the supply container as feed-water, the piston (5) carries at one of its axial ends a connecting rod (6) which engages tangentially in a toothed wheel (8) and can turn the latter by a certain angle .alpha. a defined by the piston stroke and the number of teeth of the toothed wheel (8) in a determined constant direction of rotation, wherein the toothed wheel (8) drives a mechanical valve control element with cyclic control program course, as for example a camshaft, a cam plate or the like.