Water damage in a home or building is the leading cause of microbial contamination. If not handled promptly and properly, bacteria and fungus can quickly colonize and grow, posing potential health risks for inhabitants. Health problems can occur depending upon the quality of water that causes the damage and the length of time before remediation.

There are three different categories of water quality:

• Category 1, or clean water, is the least contaminated. This category may include rainwater or broken water pipes and usually presents very little risks. However, as this water comes into contact with the ground and structures it can quickly degrade into Category 2.
• Category 2, or gray water, contains considerable amounts of chemicals and contaminants and poses a greater health risk. Examples of gray water include water from a washing machine or an aquarium. A gray water contamination, within a short period of time and exposed to temperature changes, can turn into Category 3.
• Category 3, or black water, is heavily contaminated and potentially contains sewage and other contaminants including pesticides, toxic chemicals and industrial waste. Health risks increase greatly when water damage includes black water contamination.

There are a number of different fungal contaminants commonly found in water-damaged environments. Some of the most common include certain species of Aspergillus and Penicillium. These species tend to colonize in continuously damp materials and are commonly found in house dust and on water-damaged wallpaper, wallboards, and other household materials. Other molds found after water damage can include Stachybotrys chartarum, Trichoderma, Fusarium, as well as others. These fungi prefer to colonize in extremely wet environments such as soaked wallboards and water reservoirs. All of these fungi are considered potential toxin producers and the mycotoxins from these molds can cause health effects.