The invention refers to a washing-liquid supply and dosing system, and to a method thereof, in a dishwashing machine, comprising a container (1) wherein softened water is taken in. Said container (1) is functionally separated in three compartments (V1, V2, VR) having a different volumetric capacity. The three compartments are located in sequence between themselves; the last one (V2) is filled by overflow after the first two compartments (V1, VR) have been filled and is equipped with a microswitch-operated level detecting device (S1,G1,MC1). The water fed to the first (V1) and/or third compartment (V2) is used for the washing of the crockery, whereas the water fed to the second compartment (VR) is used for resin regeneration.