Mold is a moisture problem. The only way to eliminate mold is to locate and remove the source of the moisture problem. Moisture problems can be caused by high humidity, poor ventilation systems, filled basement systems, or structural problems allowing water to enter the structure. Structural problems could be plumbing leak failed roof, or other related issues. Mold can grow in over 60% relative humidity in a building. It is absolutely necessary to fix a source of the moisture problem. This may involve fixing a roof or other part of the structure, adding the proper ventilation system(s), foundation repairs, or other types of repairs to prevent moisture water from entering the building. Mold can only start growing in the presence of water. Some mold spores will always be found in homes or in dust but they will not grow without water.