Device and method for the treatment of dampening solution for an offset printing machine

There are an apparatus and a method for the preparation of wet means (10) for an offset printing machine (44), with a cation exchanger (14) for the removal of salt-forming ions from the dampening means (10), wherein by the operation of the cation exchanger (14) of the pH of the dampening solution remains unchanged and the device on a measurement (16) of the water hardness of the dampening means (10) based control means (20) for the supply of the dampening means (10) to the cation exchanger (14).