Washing machine with electrochemical water hardness determination and method for its operation

The invention relates to a washing machine 1 with a container 2, a drum 3 for receiving laundry items 4, a drive motor 5 for the drum 3, at least one electrochemical sensor 9, 10 in the container 2 for measuring an electrochemical signal depending on a composition of an aqueous Liquid 7 in the container 2, and a control device 8, wherein the control device 8 is adapted to carry out a method comprising the following steps: (a) Provision in the container 2 of an aqueous liquid 7, the max concentration and / or a predetermined maximum detergent concentration Dirt concentration cd max does not exceed; (b) receiving at least one electrochemical signal with the at least one electrochemical sensor 9, 10; and (c) evaluating the at least one electrochemical signal measured in step (b) with respect to a water hardness in the aqueous liquid 7 using a relationship between electrochemical signals and water hardness deposited in the controller 8. The invention also relates to a method for operating this washing machine 1.