There are three main categories of water:
“Clean” water originates from a source that does not pose a substantial risk from dermal, ingestion, or inhalation exposure. Examples of clean water sources may include, but are not limited to, broken water supply lines, melting ice or snow, falling rainwater, broken toilet tanks and toilet bowls, and sink and tub overflows that do not contain contaminants or additives. Clean water that has a chance to flow through other structural surfaces and content materials may deteriorate from clean water to gray or black water if it mixes with soils and other contaminants, and as time elapses.
“Gray” water contains a significant level of contamination and has the potential to cause discomfort or sickness if consumed by or exposed to humans. Gray water carries microorganisms and nutrients for microorganisms. Examples of gray water sources may include, but are not necessarily limited to, discharge from dishwashers or washing machines, overflows from washing machines, overflows from toilet bowls with some urine (no feces), sump pump failures, broken aquariums, and punctured water beds. Gray water may contain chemicals, bio-contaminants (fungal, bacterial, viral, algae) and other forms of contamination including physical hazards. Time and temperature aggravate Category 2 water contamination levels significantly. Gray water in flooded structures that remains untreated for longer than 48 hours may change to Category 3.
“Black” water contains pathogenic agents and is grossly unsanitary. Anyone with compromised immune systems, respiratory problems or allergies, or who are under 2 years of age or elderly must remain off the job site until the building is judged safe for occupancy. Black water includes sewage and other contaminated water sources entering or affecting the indoor environment. Toilet back-flows, that originate from beyond the toilet trap, is considered black water contamination, regardless of visible content or color. Category 3 water includes all forms of flooding from seawater, ground surface water and rising water from rivers or streams. Such water sources carry silt and organic matter into structures that create black water conditions. The water is considered to be Category 3 water in situations where structural materials and/or contents have been contaminated with such contaminants as pesticides, heavy metals, or toxic substances.