After water damage, the contaminants that matter most are mold, which can grow on materials left damp; bacteria and viruses carried by sewage and floodwater; chemicals and debris in water from outside; and dust mites, which thrive in humid indoor air. In older homes, opening walls can also disturb lead-based paint or asbestos-containing materials.
- The water category decides the cleanup method
- Keep indoor humidity below 60%, ideally 30–50% (U.S. EPA)
- Pre-1978 homes need lead-safe work practices
- Health questions belong with a medical professional
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The same leak can be a simple drying job or a contamination cleanup depending on where the water came from and how long it sat. Clean water from a supply line starts out low-risk; sewage and floodwater do not.
This page explains the main contaminants in plain language. It is not medical advice — if you have health concerns, talk to a doctor.
01
Which Contaminants Come With Which Water?
| Contaminant | Typical source | What it means for cleanup |
|---|---|---|
| Mold | Any water left on materials too long | Dry within 24–48 hours; remove moldy porous materials |
| Bacteria and viruses | Sewage, toilet overflow with waste, floodwater | Containment, protective equipment, removal and sanitizing |
| Chemicals and debris | Floodwater crossing yards, roads and garages | Porous materials usually removed; surfaces cleaned |
| Dust mites | Persistently humid indoor air | Control humidity after drying |
| Lead dust | Opening painted walls or trim in pre-1978 homes | Lead-safe work practices |
| Asbestos fibers | Disturbing some older building materials | Leave undisturbed or use accredited professionals |
02
How Does Mold Relate to Water Damage?
Mold spores are naturally present indoors and out; they grow when they land on materials that stay damp. The U.S. EPA advises drying water-damaged areas within 24–48 hours and keeping indoor humidity below 60 percent, ideally between 30 and 50 percent.
03
Why Is Sewage and Floodwater Treated Differently?
Sewage and floodwater can carry bacteria, viruses and other contaminants, so they are handled as black water: containment, protective equipment, removal of porous materials that were soaked, and cleaning and sanitizing of what remains.
04
What About Lead and Asbestos in Older Homes?
Many Fairfax-area homes were built before 1978. If drying or repairs require opening painted walls or trim, EPA's Renovation, Repair and Painting rule requires paid contractors to use lead-safe practices. Some older materials may contain asbestos; EPA advises leaving undamaged materials alone and using accredited professionals when they must be disturbed.
Sources & further reading
Not sure how serious it is?
A professional assessment shows exactly where the water went and what it will take to dry and restore your property.
Frequently asked questions
Should I test for mold after a leak?
Testing is not always necessary; visible growth and moisture readings usually define the work. If you want independent air or surface sampling, an indoor environmental professional can provide it.