An adapter for a liquid container of a supply system of a wet process module for the treatment of substrates has a container part for fastening to the liquid container and a channel part for fastening to the supply system. The container part has a central opening and a fastening device for fastening the container part to the liquid container. The channel part has a continuous first channel portion and a continuous second channel portion, the first and the second channel portion each opening into the central opening of the container part.