Pressure washing a driveway, deck or siding: where the wash water is allowed to go

Pressure washing is one of the few exterior jobs where the work is easy and the disposal is the hard part. The washing takes an afternoon. The water afterwards has to go somewhere on a lot graded to send everything to the street — and that is the only part any by-law in Halton, Peel or Toronto regulates.

Where does the water on your driveway actually go?

Into a creek, then into Lake Ontario, untreated. The square grate at the curb is a catch basin, it feeds a storm sewer, and a storm sewer is a drainage pipe rather than a treatment route. Mississauga states it plainly: "Everything that goes into the storm sewer system ends up in the natural environment", and "Stormwater runoff should be made up of only rainwater and melted snow." Toronto says the same of its own catch basins: "Nothing other than rain and melted snow should ever enter a catch basin."

The sanitary sewer is the other pipe, and it goes to a treatment plant. Inside your house, every drain — sink, toilet, laundry tub, floor drain — is on it. Outside, nothing is. A bucket of soapy water poured into a laundry sink gets treated; the same bucket tipped onto the driveway reaches a creek.

Which rule applies to your house depends on who owns the pipe

There is no single GTA rule. Stormwater collection is assigned to upper-tier municipalities non-exclusively under the Municipal Act, so both a region and its towns may pass by-laws on it: the region's covers the region's sewers, the town's covers the town's. The street in front of a house is usually the town's, so the town's by-law is usually the one that reaches you.

Peel Region is worth a line, because its page can mislead a Mississauga homeowner. Peel's Wastewater By-law 53-2010 "applies to all businesses discharging directly or indirectly to sanitary sewers or storm sewers in Peel Region". The instrument that reaches a private driveway in Mississauga is the City's Storm Sewer Use By-law, whose prohibitions open with "No person shall". Peel adds that its inspectors "investigate sewer discharge complaints from industrial facilities and households".

Does this actually apply to a homeowner with a rented pressure washer?

Yes, and Milton's by-law says so in words chosen for exactly this situation. It defines "domestic waste" as effluent, discard or garbage "arising from a residence belonging to, or associated with a house or use of a house, or residential property", and puts domestic waste on the prohibited list. It separately names "carpet cleaner waste" — liquid and solid waste "generated by carpet or furniture cleaning". Neither definition has anything to do with industry.

Above all of them sits one sentence of provincial law that does not care whose pipe it is. Section 30(1) of the Ontario Water Resources Act: "Every person that discharges or causes or permits the discharge of any material of any kind into or in any waters or on any shore or bank thereof or into or in any place that may impair the quality of the water of any waters is guilty of an offence." The words "any place" are why a ditch, a swale or a creek bank at the back of a rural Milton lot is covered even where there is no storm sewer at all.

Read the penalty numbers for what they are — maximum fines available on conviction, per day, rather than tickets handed out at the curb. For a person other than a corporation, Halton's By-law 2-03 sets a maximum of $10,000 for a first offence and $20,000 for a subsequent one; Mississauga's sets $10,000 and $25,000; Peel's page mentions a ticketing system of up to $1,000. The administrative consequence is the more likely one: these by-laws let the municipality order the connection carrying the discharge stopped or disconnected until the problem is fixed, and recover its costs.

"I'm only using water" and "the soap is biodegradable"

Toronto answers the first one in a single sentence: "Power washing with water alone will still dislodge or dissolve contaminants from the surface being cleaned." Dislodging is the point of the tool. Mississauga's own list of what pollutes stormwater runoff from a property includes car soaps, "soil, grass clippings and yard waste", "oils and lubricants", "antifreeze and other fluids from cars", cooking oils and greases, cigarette butts and pet waste — and none of that stops being a contaminant because you did not add detergent.

The second one runs into a units problem. Biodegradability describes what happens to a molecule over time; the by-laws set limits on the water leaving your property today. Milton's prohibited characteristics include "visible film, sheen, foam or discolouration" — foam is named, and biodegradable soap foams. Mississauga sets the detail in Schedule A.

Federal rules do cap phosphorus in cleaning products — the Phosphorus Concentration Regulations limit a household cleaner to 0.5 per cent by weight as elemental phosphorus — but that limit is on the bottle, and Mississauga's 0.4 mg/L limit is on the water in the gutter. Meeting one tells you nothing about the other, and there is no dilution loophole either: Halton, Milton, Burlington and Mississauga all separately prohibit adding water to a discharge in order to meet their limits.

So what do you do with the water?

Toronto publishes the shortest usable answer, in three options: let the water evaporate, re-route it away from a catch basin or contain it, or dispose of it in an indoor drain or haul it off-site. Hauling off-site has to be done by a hauler approved by the Ministry of the Environment, Conservation and Parks, which puts it into a contractor's quote rather than a Saturday job. That leaves evaporation, containment and the indoor drain.

1. 1Sweep first, and sweep properlyMississauga's advice is to "vacuum, sweep, and use rags or dry absorbents on your driveway to control spills instead of hosing it down", and Toronto's is to "sweep sidewalks and driveways clean instead of using a running hose". Dry removal costs nothing, both cities ask for it, and every gram of grit you sweep up is a gram that never has to be contained or collected later.
2. 2Stand at the bottom of the slope and find where the water will goBefore any water runs, walk the low edge of the surface you are about to wash and locate every grate, gutter line, swale and ditch it drains to. If the surface drains straight to the curb, that route has to be blocked or the water collected before you start.
3. 3Move what you can onto ground that absorbsToronto's recommendation for washing a car is to work on a permeable surface such as gravel, so the water is absorbed before it reaches the storm sewer. The same applies to furniture, cushions, bins and mats — Mississauga asks directly that you "avoid washing carpets, outdoor furniture and other items on the driveway".
4. 4Block the route, do not just aim away from itWhere the surface cannot be moved — siding, a fixed deck, the driveway itself — the water has to be stopped before the grate: a berm, a rolled towel or sandbag dam at the low edge, or a covered catch basin, then wet-vacuuming or pumping what collects.
5. 5Send the collected water to an indoor drainA shop vacuum emptied into a laundry tub or toilet puts the water on the sanitary system, which is where Toronto says household wash water belongs. Let heavy grit settle in the pail first and bin the sludge instead of pouring it down the drain.
6. 6Check the forecast before you startRain in the hours after you wash carries anything still lying on the surface straight to the catch basin. Mississauga applies the same reasoning to pool water, which may not be discharged within 24 hours of a storm event.

When the honest answer is to not wash it at all

On some lots containment is not realistically achievable with household equipment: a short driveway that falls hard to the street with the catch basin at the bottom, a townhouse with no permeable ground to work over, a semi where the neighbour's grade takes the runoff first. There the choice is between doing the job with proper containment and not doing it, and leaving a driveway grey for another year costs nothing.

• Dry sweeping raises no disposal question at all, and both Toronto and Mississauga ask for it. Do it, then look at what is actually left before reaching for a hose.
• A mark that returns in the same spot every autumn is worth tracing to its source before washing it. If the same strip of driveway or the same corner of siding greys up each year, look at what is dripping onto it — see sump pump and downspout checks before the first heavy autumn rain.
• Washing a deck late in the season leaves it wet going into freeze-up. If a deck or fence is on the autumn list, the sequencing matters as much as the cleaning; decks and fences before winter sets out what September is for.
• Glass is a different job with a different tool. Every Season's window cleaning uses a pure-water pole system where suitable rather than a pressure washer.

If you hire someone, the liability does not transfer

This is the part worth knowing before you book anyone, and Toronto states it without hedging: "both the person hiring and the mobile wash business operation/company are responsible for wastewater discharging from the property." Toronto's definition of a mobile wash business is broad and explicitly includes "landscapers washing windows" alongside companies that wash cars and buildings. Burlington's by-law works the same way from the other end — where a contravention has occurred on a premises, the owner of that premises is presumed to have caused or permitted it. Five questions cover it:

1. Where will the wash water end up on my property, and which drain is nearest to it?
2. Will you be containing and removing it, letting it soak into ground away from a drain, or letting it run?
3. If it is being hauled away, who hauls it, and are they approved by the Ministry of the Environment, Conservation and Parks?
4. Is dry removal — sweeping and vacuuming — part of the work before any water is used?
5. If something does reach a catch basin, who is calling it in?

On that last point: in Toronto, anything other than rain or melted snow entering a catch basin is "considered a spill", and the City's instruction is direct — "If you suspect a spill, please contact 311 immediately." Agree in advance who makes that call, so it is not being decided while the water is running.

The one residential discharge that has written permission, and what it tells you

Mississauga's by-law prohibits residential pool water from storm sewers and then carves out a single exception, with conditions attached: the water has to be held in the pool, spa or hot tub "for at least 7 days after the last dosage of chlorine or other chemical treatment", copper and chlorine have to be at or below the Schedule A limits, the discharge has to be "by way of slow, controlled discharge to the curb in front of the owner's premises", and it may not happen within 24 hours of a storm event.

Read that as a benchmark. Pool water is nearly clear and contains one known chemical, and it still needs a week of waiting, a concentration limit, a controlled flow rate and a dry-weather window before it may touch a storm sewer. Wash water off a driveway is cloudy, carries soap and sediment, and has no exception written for it anywhere.

Storm drains are worth checking in autumn for a separate reason that has nothing to do with washing — see leaf-clogged catch basins for the ten minutes that keeps water off your property.