An indoor environment has everything mould spores need to grow — the right temperature and a food source such as drywall, plywood, etc. It only needs moisture or a water source. Mould will grow if a moisture source is introduced into the environment. Water intrusions from an outdoor source, like flooding or roof and window leaks, or an indoor source, like broken plumbing lines, need to be properly repaired and the area cleaned and dried within 48 hrs or mould growth can occur. Mould will continue to grow, or re-emerge, as long as the moisture source remains. Any material damage or health concerns will also continue to occur.