This is water rising from the ground into the home, through or round a broken damp proof course (DPC) or passing through the brickwork if the property was built without one. (A DPC is a horizontal layer of waterproof, material built into the buildings’ walls just above ground level)
Rising damp only affects basements and ground floor rooms. Normally it won’t rise more than 12-24 inches (300-600mm) above ground level and normally leaves a tide mark low down on the wall with white salts on the affected areas.
Rising damp will be present all year round but is more noticeable in winter. Left untreated, it can cause wall plaster to crumble and paper to lift in the affected area.
Note – Black mould is rarely seen where there is rising damp (and then only in the early stages) because rising dampness carry natural ground salts which prevent the growth of black mould.