A litre a day isn't unusual- of course it all depends on the size of your unit, the humidity in the room and the source of the damp. The room should dry out completely in a week or so and the machine switch itself off. If you continuously get a litre a day there is a structural problem which could be anything like a failed damp course, poor pointing, leaking pipework or a leaking gutter.
We have stone walls here and 3 dehumidifiers. Two small units are used rarely (when 70% is reached) and one larger unit, which can theoretically take out 5 litres a day, is left on at 40% in a large bathroom which then doubles as a drying room.
Problem with dehumidifiers is they ice up if the room is too cold and then run with no effect, so worth watching for that if the room is unheated PK, otherwise you will simply be wasting electricity.