For significant mold growth to occur, there must be a source of water and a substrate capable of sustaining the growth. Many common building materials, such as drywall, wood, carpets, and carpet padding are capable of sustaining or contributing to mold growth.
Since common building materials are capable of sustaining mold growth and mold spores are ubiquitous, mold growth in an indoor environment is typically related to an indoor water or moisture problem. Leaky roofs, building maintenance problems, or indoor plumbing problems can lead to mold growth inside homes, schools, or office buildings. Another common source of mold growth is flooding.