Rising damp
This is caused by water rising from the ground into the home. Rising damp can only affect basements and ground floor rooms, and will normally rise no more than 12 to 24 inches (30 - 60 cm) above ground level. It usually leaves a ‘tide mark’ low down on the wall. You may also notice white salts on the affected walls.
Rising damp is more noticeable in winter, but will be present all year round.
Black mould will rarely be seen with rising damp, because the damp carries ground salts stopping its growth. If there is black mould, it will only be found in the early stages.