Where does pressure washing water go? Storm drains, runoff and the rules
Updated · KeystoneProGuide editorial team
Where does the water from pressure washing go?
Wherever it runs, and the official guidance assumes that much of it reaches a drain. The U.S. Environmental Protection Agency (EPA) explains that water flowing over roofs, streets and parking lots goes into a water body or a storm drain, and that because it flows over hard surfaces, there is no opportunity for soil and plants or a water treatment facility to filter out pollutants. The EPA is describing rain, but the same pavement carries wash water.
What happens next depends on the kind of sewer under your street.
What is the difference between a storm sewer and a combined sewer?
Pennsylvania's urbanized areas are required to be in the state's program for separate storm sewers, according to Penn State Extension. Penn State Extension says a separate storm sewer system gathers water from developed areas and discharges it, without treatment, into local streams and rivers; it is not connected to the sanitary sewer that takes household wastewater to a treatment plant.
Some places have combined sewers, which carry stormwater and sewage in the same pipes. Penn State Extension says some Pennsylvania communities have them, and the EPA says such systems are designed to overflow in heavy rain or snowmelt, sending untreated sewage to nearby streams. Philadelphia is one: the Water Department says its combined system serves about 60 percent of the city, and that this older section often overflows in wet weather.
Either way, a storm inlet is not a route to treatment you can rely on. The Philadelphia Water Department puts it in a sentence: only rain should go in storm drains, because drains lead to streams and rivers. Its list of things to keep out includes mop water and vehicle oil.
What do Pennsylvania's rules say?
The state's storm sewer program, run by the Department of Environmental Protection under the federal Clean Water Act, requires each participating municipality to carry out six measures. One is illicit discharge detection and elimination, which Penn State Extension describes as keeping things other than stormwater out of storm sewer inlets. Its examples of illicit substances include laundry wash water, paint and automobile oil.
Participation is widespread here. Penn State Extension says around 950 municipal systems were enrolled statewide by 2018, and the Delaware County Conservation District says every municipality in Delaware County is required to hold a permit. Each municipality writes its own program, so the place to ask what is allowed on your street is your township, borough or city.
No state or Philadelphia page found for this guide deals with water from washing a house in particular. The guidance above is general, and it is the basis for the questions at the end.
What if the house has old paint?
Then the water itself is part of the lead rule. The EPA's archived answer on pressure washing says a lead-safe certified firm must isolate the work area so that no dust or debris, including in the waste water, leaves it, and that it is important to dispose of waste water from pressure washing properly. It tells firms to check with the local water treatment authority. Its guidance for do-it-yourselfers lists dirty water among the waste to collect and control. Pressure washing an older painted house covers the rest of the rule.
What about chemicals and oil?
Two documented cases show why they matter. Connecticut's consumer protection department described a driveway sealing scam in which unregistered crews used hot motor oil instead of sealant; the oil washed away after a couple of rainstorms, polluting water systems. And the National Park Service, writing about cleaning oil from buildings, says the waste should be collected on drop cloths or other devices so that the ground or water is not re-contaminated.
For cleaners, see cleaning chemicals and bleach, which covers what the labels and the EPA say.
Does the trade recognize the issue?
Its main trade association does, in its own words. Power Washers of North America describes an environmental course that teaches contractors the Clean Water Act requirements and EPA regulations that govern wastewater discharge, along with methods for reclaiming and containing wash water. That is the association's description of its training, not a statement of the law, but it shows that water handling is something a trained company can be asked about.
What should you ask a company?
- Where will the water from my job drain?
- Will you collect or contain it, and if so, where will it be disposed of?
- What will be in it: detergent, bleach, old paint, oil?
- Have you checked what my municipality allows?
- On a house built before 1978, how will you keep the waste water inside the work area?
Ask for specifics rather than a general reassurance. Questions to ask before you hire has the full checklist, and businesses offering the service are on the pressure washing directory page.
Sources
- Sources and Solutions: Stormwater, U.S. Environmental Protection Agency
- What is an MS4?, Penn State Extension
- Taking Care of Storm Drains, Philadelphia Water Department
- Green City, Clean Waters, Philadelphia Water Department
- Stormwater Info, Delaware County Conservation District
- How do RRP requirements apply to pressure washing? What containment and other preparation are required?, U.S. Environmental Protection Agency (January 2025 archived copy)
- Lead-Safe Renovations for DIYers, U.S. Environmental Protection Agency
- Protecting Historic Structures from Oil Contamination, National Park Service
- Officials Remind Consumers to be Cautious Before Beginning Home Improvement, Driveway Resealing Projects, Connecticut Department of Consumer Protection
- EPA Environmental Compliance Training, Power Washers of North America (PWNA)