To provide a supplying method of dampening water which prevents deterioration of the dampening water in long-time continuous printing or restarted printing after interruption and enables continuous reuse of the dampening water in a good state without disposing of it.

The supplying method of the dampening water for reusing the dampening water used for offset printing comprises the process of collecting the dampening water from a printing unit, the process of filtering and sterilizing the dampening water collected by the process of collecting it, the process of storing only the dampening water sterilized by the filtering and sterilizing process, and the process of supplying the dampening water which prepares the dampening water by mixing the dampening water sterilized by the filtering and sterilizing process, a dampening water concentrate and water.