Water damage categories explained: clean, grey and black

Not all water damage is the same. A leak from a supply line puts drinkable water on the floor. A backed-up toilet puts sewage there. Treating them the same way would either waste a lot of salvageable material or put people at risk.

The restoration industry's standard, ANSI/IICRC S500, sorts water into three categories by contamination. ^[1] In everyday terms they are clean water, grey water and black water. The category guides decisions about protective gear, what gets removed and how surfaces are cleaned.

Clean water comes from a source that was safe to drink: a supply line, a faucet, a water heater. It is the best case. If it is extracted and dried quickly, carpet can often be kept (the pad is often replaced), drywall that was wet briefly can be dried in place and wood can often be saved.

Clean water does not stay clean. As it sits, it picks up dirt and contaminants from floors, wall cavities and the ground under a crawlspace, and bacteria begin to grow. After a day or two, a clean-water loss may be handled more like grey water. That is one reason the EPA's 24 to 48 hour drying window matters.

Grey water carries some contamination that could make people sick if ingested. Washing machine and dishwasher discharge, a toilet overflow with urine but no feces and some sump overflows fall here.

Crews wear gloves and handle porous materials more cautiously. Carpet pad is usually replaced, and carpet and drywall may be removed depending on how long they were wet. Surfaces are cleaned before drying. Grey water left standing for long enough can become black water.

Black water is grossly contaminated. Sewage backups, toilet backflow with feces and floodwater from rivers and creeks are the usual sources. In Oregon, that includes basement floor drain backups during storms and water from overflowing creeks such as Johnson Creek in Portland or Bear Creek in the Rogue Valley. Floodwater can carry sewage, fuel and chemicals as well as bacteria.

The EPA says sewage-related water damage should be handled by experienced professionals. Porous materials that black water touched, such as carpet, pad, drywall and insulation, are generally removed, and everything that stays is cleaned and disinfected before drying. See sewage backup cleanup.

The category affects what a contractor removes, how long the job takes and how the work is documented. A contractor should tell you which category they are treating your water as and why.

It can also affect insurance. Policies often treat sewer backups and flooding differently from sudden plumbing failures. Read your policy and see working with your insurance adjuster.

Some situations sit between categories. Rain coming through a roof starts clean but picks up whatever is in the attic insulation and on the roof deck. A sump pit overflow may be mostly groundwater or may include water from a laundry tray that drains into it. A toilet that overflowed once and was mopped up quickly is different from one that ran for hours across a carpeted floor.

Contractors judge these by the source, what the water passed through and how long it sat. When the answer is unclear, they generally err toward the more cautious category, because the people living in the house bear the consequences of a wrong call.

A supply line bursting in a Bend garage after a sub-zero night is a classic Category 1 loss, provided it is caught quickly. A washing machine overflowing in a Beaverton upstairs laundry is usually Category 2. Water seeping into a Portland basement after weeks of rain is often treated as Category 2, and becomes Category 3 if it came up through the floor drain or carried sewage. Floodwater from a creek in Eugene or Medford is Category 3.

Knowing which one you are dealing with helps you understand why a contractor wants to keep or remove particular materials.

Category also guides decisions about contents. After clean water, most hard items and many fabrics can be cleaned and dried. After grey water, washable fabrics can usually be laundered in hot water, while upholstered furniture and mattresses are judged case by case. After black water, porous items such as mattresses, upholstered furniture, stuffed toys and cardboard are generally discarded, and food, medicine and cosmetics it touched should always be thrown out.