Abstract: In summary, the invention proposes to provide two different conversion modes for determining the water hardness on the basis of the conductivity of raw water in a water softening device (1) dividing influent raw water volume flow V(t)raw into two partial volume flows V(t)partial1soft V(t)partial2raw, subjecting a partial volume flow V(t)partial1soft to a full softening process and re-uniting the two partial volume flows thereafter again into an admixed water volume flow V(t)admixed. Conversion using a first calibration curve (F1) is conservative and reflects the maximum water hardnesses occurring at different conductivities; this conversion mode is used for automatically controlling the regeneration of an ion exchange resin (5), with the capacity of the ion exchange resin being known. The conversion using a second calibration curve (F2) is close to reality and reflects the average water hardnesses (i.e.

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.