Clean, Grey and Black Water: The 3 Categories of Water Damage

The three categories of water damage describe how contaminated the water is. Category 1 is clean water from a sanitary source such as a supply pipe. Category 2, called grey water, carries enough contamination to make someone sick. Category 3, called black water, is grossly contaminated and includes sewage and floodwater from outside. The category decides what can be dried in place and what has to be removed.

Where the categories of water damage come from

The categories are defined in the IICRC S500, the standard that restoration companies in Canada and the United States work to. They exist so that everyone on a job, including the homeowner, the restorer and the insurance adjuster, is using the same terms when deciding how to handle wet materials. The category is about the water. It says nothing about how much water there is or how hard the job will be to dry.

Category 1: clean water

Clean water comes from a sanitary source and poses no substantial risk from skin contact or accidental swallowing. Typical sources:

• A burst or leaking water supply pipe.
• A failed supply hose to a washer, dishwasher, toilet or fridge.
• A toilet tank or a tub or sink overflow with no contaminants.
• A leaking water heater.
• Melting ice or snow, and rainwater that comes straight in without passing through soil or dirty building materials.

With clean water caught early, the aim is to dry and save as much as possible. Carpet, drywall and framing can often be dried in place.

Category 2: grey water

Grey water contains significant contamination, chemical or biological, and can cause discomfort or illness if a person swallows it or it gets into a cut. Typical sources:

• Discharge from a dishwasher or washing machine.
• A toilet bowl overflow that contains urine but no feces.
• Water from an aquarium or a waterbed.
• Water that has leaked through building materials and picked up contamination along the way.

Grey water jobs call for gloves and protective gear, cleaning as well as drying, and a harder look at porous materials. Carpet underpad that was wet with grey water is normally discarded, and surfaces are cleaned before drying equipment goes on.

Category 3: black water

Black water is grossly contaminated and can contain disease-causing organisms and other harmful agents. Typical sources:

• Sewage, including any backup from the drain line beyond a toilet's trap.
• Floodwater from rivers and streams.
• Surface water that has run across the ground and into the house.
• Water rising from the ground that carries soil and whatever is in it.
• Any water that has sat long enough to support heavy microbial growth.

The black in the name refers to contamination, not colour. Black water can look perfectly clear. With this category, porous materials that got wet, such as carpet, pad, drywall and insulation, are removed. The remaining structure is cleaned and disinfected, and only then dried. The work is done under containment with protective equipment.

How clean water becomes grey or black

A category is a snapshot, and it can get worse. Two things push it down the scale. The first is time. Clean water sitting in carpet or a wall cavity at room temperature starts growing bacteria, and after a couple of days it is no longer treated as clean. The second is contact. Clean water that runs through a dirty crawlspace, across soil or through old insulation picks up what it touches. Warm conditions speed both up.

This is the main reason speed matters with a supply-line leak. On day one the wet carpet and drywall may be salvageable. Left for several days in a warm house, the same materials may have to come out.

What the category means for your home

In practical terms, the category answers four questions: whether you can safely handle the cleanup yourself, what protective gear is needed, which materials stay and which go, and whether cleaning has to come before drying. A second S500 term, the class of water loss, is a separate measure of how much material is wet and how much drying capacity is needed, and it should not be confused with category.

When we assess a job, we identify the source, how long the water has been there and what it passed through, then write the category into the quote along with the moisture readings. Send photos and a firm written quote comes back within 2 hours, between 7 am and 9 pm. Most water damage jobs here run $1,950 to $11,000.

If you have water in the house right now, write down two things before you do anything else: where it came from and when you first noticed it. Those two facts set the category.

Common questions