Black mould is generally due to a condensation or plumbing issue. If it is confined to one area on an internal wall will likely be due to plumbing leaks.
If the mould is more widespread and appearing in various different areas then the likely cause is condensation. Mould can simply be cleaned off using a weak solution of bleach and water. However if the cause is condensation, then your would need to look at ventilation to the property.
In this case it would be prudent to improve the ventilation to the water making areas by the installation of good quality extractor fans. Preferably humidity activated models. These fans sense the humidity within the air and activate at a preset level to ensure access vapour is removed. In my experience Nuaire are the best models. Take a look at their website.
Peter Barber CSSW,.CRDS.