Pressure Washing Parking Garages and Lots: Where Can the Wash Water Go?
Wash water from pressure washing a parking garage or lot can't go into a storm drain. Depending on the city, it goes to the sanitary sewer with the property owner's permission (and sometimes a permit or grit trap), gets hauled to an approved facility, or is treated before release. In practice that means sweeping first, blocking drains and recovering the water with a vacuum as you wash.
Parking surfaces carry oil, grease, metals and grit, which is why cities single them out. Fort Worth says parking lots and gas stations usually don't qualify for its storm drain exemptions for exactly that reason. If you wash garages, decks, drive-thrus or lots for property managers, the water plan is part of the job.
Why is parking garage wash water treated as a pollutant?
Storm drains go straight to creeks and rivers with no treatment. Garage floors collect drips of oil and coolant, tire dust and road grit, and pressure washing puts all of it into the water. The City of Corona, California, notes that wash water can carry dirt, soap, oil and grease even when cleaners are labeled nontoxic or biodegradable.
Garages add a twist: their floor drains may not go where you think. Fort Worth warns that many outdoor floor drains connect to the storm sewer, so confirm the plumbing before you send water down one.
What do California and Texas cities require?
City | Storm drain | Sanitary sewer | Other rules |
San Diego, CA | Never | Private connection only (sink, toilet, cleanout), max 20 GPM, owner's permission | No sewer permit under 2,500 gal/day of exterior wash water; penalties up to $10,000 per day |
Corona, CA | Prohibited | For parking areas, only with owner's permission and after dry pre-cleaning | Berms, drain covers and vacuums to contain water |
Fort Worth, TX | Parking lots usually not exempt | Owner's permission; free of grease and grit; at or below 150°F; pH 5.0–12.0 | Business permit and per-unit registration; manholes forbidden; fines up to $2,000 per day |
Grand Prairie, TX | Prohibited, except plain water from lot washing | Through an approved sand/grit trap | Active recovery required off approved wash stations; recycling units must submit test data |
Austin, TX | Never | Collect and send to sanitary sewer; otherwise haul to a permitted facility | Seal or plug inlets; use wash mats and barriers |
San Antonio, TX | Not addressed as an option | Via a pretreatment system, or manifest through a certified hauler | Power washers working for pay must register with SAWS |
Sources: San Diego mobile business guide, Corona pressure washing BMPs, Fort Worth, Grand Prairie, Austin, San Antonio Water System.
Rules change and vary by city, so call the local stormwater office and sewer utility before you bid a job.
How do you pressure wash a parking garage the right way?
Dry clean first. Sweep or blow off loose debris. Corona requires successful dry pre-cleaning before parking area wash water can go to the sewer.
Spot-treat oil. Soak up oil and grease spots with absorbent before you wash; Fort Worth calls for absorbent clay on spills.
Block the drains. Cover or plug storm drain inlets and confirm where floor drains lead.
Wash and recover together. A surface cleaner paired with a recovery vacuum picks up water as you go instead of chasing puddles.
Don't leave water to evaporate. San Diego says not to leave wash water on pavement to dry, and to sweep up remaining solids.
Dispose the approved way. Use a permitted sewer connection, a grit trap or a licensed hauler, and keep records.
Does hot water help on garage floors?
Yes. Oil and grease release faster with heat, so hot water cleans with fewer passes and less detergent, which means less water to recover. Some cities limit heat, though: Fort Worth's storm drain exemptions need prior city permission for water above 110°F, and its sewer discharges are capped at 150°F. See hot water vs. cold water pressure washers for when heat is worth it.
Should you recycle wash water on big garage jobs?
On large decks and multi-level garages, recycling cuts the number of fill-ups and the volume you have to dispose of. Check local rules first: Grand Prairie requires companies using recycling units to filter water at least one cycle and submit test data for oil and grease, metals and volatile organic compounds, and Fort Worth asks recycling operators to map their sewer discharge points and test at least once per permit term.
What equipment does a garage and lot washing crew need?
A hot water pressure washer sized for flow, since rinsing large slabs is a GPM job (PSI vs. GPM).
A wide surface cleaner to cover square footage evenly.
A recovery vacuum and holding tank, plus drain covers and berms.
Optional recycling for big or repeat jobs.
For an example of a wide surface cleaner with built-in recovery, see the 8' surface cleaner with wash water recovery build on Hot And Mighty Direct. If you already own a washer, read adding wash water recovery to your existing pressure washer.
Frequently asked questions
Can I wash a parking garage into its floor drains?
Only if you've confirmed the drains go to the sanitary sewer and the owner and sewer utility allow it. Many floor drains connect to the storm sewer, which is off limits.
Is plain water without soap allowed to run off?
Sometimes. Grand Prairie allows plain water from parking lot washing to reach the storm sewer, but Fort Worth says parking lots usually don't qualify for its exemptions. Ask your city.
Who is responsible if wash water reaches a storm drain?
The washing company, and sometimes the property owner too: Contra Costa County says the businesses that hire a cleaner are ultimately responsible for their contractor's discharges. Get the owner's permission for any sewer discharge in writing and keep disposal records.
Do I need a permit to pressure wash commercially in Texas?
In some cities, yes. Fort Worth requires a business permit and registration for each wash unit, and San Antonio requires paid power washers to register with SAWS.
Talk to us about your next rig
Hot And Mighty has 50+ years of experience building hot water wash, recovery and recycling systems, delivered nationwide. Tap "Text us" on this page or call 800-897-7515, Monday to Friday 9 to 5 EST, and tell us what surfaces you wash and where.
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