Category 1. This is liquid from a clean and sanitary source, such as faucets, toilet tanks, drinking fountains, etc. But, category one can quickly degrade into category two.
Category 2. This category of liquid used to be called grey water, and is described as having a level of contaminates that may cause illness or discomfort if ingested. Sources include dishwasher or washing machine overflows, flush from sink drains, and toilet overflow with some urine but not feces.
Category 3. This is the worst classification and is grossly unsanitary. It could cause severe illness or death if ingested. It used to be called black water, and sources include sewer backup, flooding from rivers or streams, toilet overflow with feces, and stagnant liquid that has begun to support bacterial growth.
Class 1. The lowest and easiest to deal with, this has a slow evaporation rate. Only part of a room or area was affected, there is little or no wet carpet, and the moisture has only affected materials with a low permeance rate, such as plywood or concrete.
Class 2. With a fast evaporation rate, this level affects an entire room, carpeting, or cushioning, the wetness has wicked up the walls at least 12", and there is moisture remaining in structural materials.
Class 3. This class has the fastest evaporation rate, and ceilings, walls, insulation, carpet and sub-floors are all saturated. The liquid may have come from overhead.
Class 4. This class is labeled as specialty drying situations, which means there has been enough liquid and time to saturate materials with very low permeance, such as hardwood, brick, or stone.