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Almost certainly more than it looks. Clarity is a poor guide — sewage backing up through a floor drain often runs clear, and groundwater that has crossed a yard carries plenty you cannot see. The reliable answer comes from where the water came from and how long it has been there.
The three categories
Restoration practice classifies water by contamination rather than appearance, and the category determines what can be saved.
Category 1, clean water. From a sanitary source with no significant contamination at the moment of release — a supply line, a water heater, a burst pipe, an overflowing tub of clean water. Lowest risk.
Category 2, grey water. Contains meaningful contamination and can cause illness on contact or ingestion. Washing machine or dishwasher discharge, toilet overflow containing urine but no solids, or clean water that has sat long enough to grow bacteria.
Category 3, black water. Grossly contaminated. Sewage, toilet backflow beyond the trap, floor drain backup, and any water that has crossed ground outdoors. Requires containment and protective equipment.
Categories degrade over time
This is the point most people miss. A clean-water loss does not stay clean. Temperature, time, and whatever the water contacts move it up the scale — clean becomes grey, and grey becomes black.
There is no universal clock, because it depends on temperature, materials, and what was already in the space. But the direction is one-way, and it means a burst pipe discovered promptly and the same burst pipe discovered after a weekend away are genuinely different jobs with different salvage outcomes.
This is the strongest practical argument for responding immediately. Delay does not simply spread damage — it changes the category, and the category decides what leaves the building.
Judging your own situation
Assume category 3 if water came through a floor drain or toilet, if it entered from outdoors across ground, if there is any sewage odour, or if it has been standing more than a couple of days.
Assume category 2 at minimum if the source was an appliance discharge, or if clean water has been sitting for a day or more.
Category 1 is reasonable only when you can identify a clean source with confidence and the response is immediate.
When in doubt, treat it as the worse category. The cost of over-caution is some material discarded unnecessarily. The cost of under-caution is exposure and contaminated material left in the building.
What the category changes
Category 1 permits drying most materials in place, with the carpet pad usually the exception. Category 2 means porous materials come out and what remains is cleaned and treated. Category 3 adds containment, protective equipment, negative air pressure, and regulated disposal.
It also changes the timeline and the invoice, which is why the source question comes before any discussion of price.
What appearance does not tell you
Clear water can be sewage. Dirty-looking water can be silt-laden groundwater with modest contamination. Odour is a useful signal when present but its absence proves nothing.
Testing exists but is rarely the practical route. The source and the elapsed time answer the question faster and more reliably than looking at the water.
Related pages
For sewage response, see sewage backup in a basement. For health considerations, see health risks after a basement flood. For salvage decisions, see wet materials and belongings.