A system for treating liquids comprising: a fluidics unit having at least one functional unit; at least one liquid storage unit of the first type; at least one liquid storage unit of second type; a first liquid line; and a second liquid line, wherein a flow of liquid through the first liquid line directed from the fluidics unit to the liquid storage unit of first type is blocked, at least at times, by means of a first valve and a flow of liquid through the second liquid line in the direction from the liquid storage unit of second type to the fluidics unit is blocked, at least at times, by means of a second valve.