Where Parking Garage Wash Water Is Allowed to Go

Water used to wash a parking garage deck is not clean water. It carries oil, antifreeze, brake dust, tire particles, de-icing salt and whatever detergent was used, so in most North American cities it may not be sent to a storm drain. It has to be captured and either discharged to the sanitary sewer under local rules (often after an oil-water separator) or hauled away, and the cheapest way to stay compliant is to sweep first so there is less to wash.

This guide covers how the rules are structured in the US and Canada, what a compliant washdown looks like on a real deck, and the questions that keep a property manager out of trouble when a contractor shows up with a pressure washer.

Why the storm drain is off limits

Storm drains in most cities run straight to a river, lake or harbour with little or no treatment. Sanitary sewers go to a treatment plant. That split drives almost every rule on this topic.

In the United States, the Clean Water Act prohibits discharging pollutants to waters of the US without a permit, and the NPDES stormwater program requires municipalities with separate storm sewer systems (known as MS4s) to ban illicit, non-stormwater discharges. Commercial wash water is one of the examples the EPA lists as a non-stormwater discharge. So the actual rule your property answers to is usually a city or county illicit discharge ordinance, written to satisfy the city's own MS4 permit. Fines and cleanup costs are set locally.

In Canada the structure is different but the outcome is similar. The federal Fisheries Act prohibits depositing harmful substances into water frequented by fish, and municipalities regulate what goes into their sewers through sewer use bylaws. Toronto's is Chapter 681 of the Municipal Code. Metro Vancouver has its own sewer use bylaw, and in Greater Montréal the Communauté métropolitaine de Montréal sets wastewater discharge rules that member cities apply. These bylaws typically limit oil and grease, suspended solids and certain chemicals going into the sanitary system, and forbid anything but rain and snowmelt going into the storm system.

None of this is a reason to stop washing a garage. It is a reason to plan the wash.

What counts as a problem discharge

The rule of thumb most stormwater inspectors use is simple: if it is not rain, it should not be in the storm drain. On a parking deck that includes:

• Pressure washing or scrubbing runoff, with or without detergent
• Water from cleaning up a fuel or oil leak
• Rinse water carrying salt and sand after winter
• Degreaser applied to stained stalls and ramps
• Slurry from a ride-on scrubber that was dumped into a floor drain

Even plain hot water becomes a pollutant once it has picked up a winter's worth of grime off the concrete. "We didn't use soap" is not a defence in most ordinances.

Find out where your drains go first

Before any wet cleaning, someone needs to know which drains on the property connect to what. Older garages in particular can be confusing:

• Top decks exposed to weather usually drain to the storm system.
• Covered levels may drain to the sanitary sewer, sometimes through an oil-water separator or sand interceptor, and sometimes not.
• Ramps and entrances often have trench drains that tie into storm lines.

The building's mechanical drawings or the original plumbing permit will usually show this. If nobody has them, a plumber can dye-test the drains. Marking storm drains on site (a stencil or a simple sign) helps every contractor who works on the deck after that.

What a compliant washdown looks like

A properly planned garage wash has a few parts that are easy to check on the day.

Dry sweep before any water

A ride-on sweeper picks up the bulk of the sand, salt, litter and loose grit dry. That debris goes in a dumpster, not into the wash water. In spring, after a Canadian or northern US winter, this one step removes most of what would otherwise turn into muddy slurry. It also shortens the wash itself.

Block the storm inlets

Storm drains in the work area get covered with drain mats or plugged with inflatable drain plugs before washing starts. Berms or water-filled booms keep the water where the crew wants it.

Recover the water

The wash water is collected with a vacuum recovery unit or a scrubber that picks up as it goes. Recovered water is then handled one of two ways, depending on local rules: discharged to a sanitary connection the city allows (often through the building's own separator, sometimes only with permission), or pumped into a tank and hauled to an approved facility.

Treat stains separately

Heavy oil stains are spot-treated with absorbent and degreaser, and the residue is collected as waste rather than washed across the deck.

Keep a record

A short log of the date, area, drains blocked, volume recovered and where it went is useful if an inspector ever asks. Many property managers keep it with their stormwater or environmental file.

How sweeping frequency changes the picture

Garages that are only washed once a year collect a lot of material between washes, and the spring cleanup becomes a large, wet job. Regular dry sweeping, weekly or every two weeks in busy structures, keeps grit, salt and litter off the deck so the annual wash is lighter and produces less dirty water to manage.

Frequent sweeping also helps with things inspectors and insurers look at for other reasons: slip hazards on ramps, sand build-up near expansion joints, and debris clogging the drains that do need to work. Our guide to parking garage sweeping in Cincinnati goes into scheduling in more detail.

Questions to ask a contractor before they wash

• Will you sweep before washing, and what happens to the dry debris?
• How will you protect storm drains in the work area?
• Do you recover the wash water, and with what equipment?
• Where does the recovered water go, and who confirmed that is allowed here?
• What detergents or degreasers will you use, and can we see the safety data sheets?
• Who is responsible if a discharge happens during the job?

A contractor who answers these clearly and in writing is easier to defend if something goes wrong. One who plans to "just rinse it toward the drain" is the risk.

Frequently asked questions

Can you pressure wash a parking garage into the storm drain?

In most US and Canadian cities, no. Wash water from a parking structure is treated as a non-stormwater discharge, and local illicit discharge ordinances or sewer use bylaws prohibit sending it to the storm system. It needs to be recovered and sent to a permitted sanitary connection or hauled away.

Does using only hot water and no detergent make it allowed?

Usually not. The water picks up oil, metals, salt and sediment from the deck, and those are the pollutants the rules are written for. Some cities have narrow exceptions for specific activities, so check your local ordinance, but plain water on a dirty garage deck is generally not exempt.

Who is responsible if a contractor's wash water reaches a storm drain?

It depends on the local rule and your contract, but property owners are often named along with the contractor. That is why it is worth putting drain protection, water recovery and disposal in the written scope rather than leaving it to the crew on the day.

How often should a parking garage be swept?

Busy commercial and mixed-use garages are commonly swept weekly, with ramps and entrances done more often in winter. Lower-traffic structures may do well on every two weeks or monthly. The right frequency depends on traffic, weather exposure and how much salt and sand comes in on vehicles.

Plan the sweep and the wash together

Broomline sets up scheduled ride-on sweeping routes for parking garages and industrial floors, with washdowns scoped so the water is handled properly. Tell us about your structure, its levels and your drain layout through the quote form, or see the cities we serve. We reply with next steps and a written proposal for your site.