Washing buildings and surfaces under Wisconsin's permit

Building wash water carries what came off the building

Building washing gets its own rule because the solids that come off a wall are not just dirt. The permit names paint and other particles that may contain toxic substances.

When washing produces solids like these, you must do one of two things before you start. Prevent direct discharge to surface waters as far as feasible and divert the water to a holding tank or sanitary sewer. Or send it to grass, soil or gravel to infiltrate.

With the second option, you then collect the solids after the water soaks in. They are disposed of as solid waste.

Building washing that produces solids such as dirt or paint must divert to a holding tank or sanitary sewer, or infiltrate and collect the solids. — Wisconsin DNR, Low-Impact Discharge general permit WI-0066575-01-0, retrieved 2026-09-29

Concrete, decks and lots share the paved-surface rule

Flatwork is where crews meet the impervious-surface rule most often. Patios, driveways and parking lots all count.

Before washing, do one of three things. Direct the water to a settling basin, tank or other settling device. Temporarily block or plug channeled flow to storm sewers and let solids settle. Or direct the water to grass, soil or gravel where it can infiltrate.

Pick the step that fits the site and write it into the plan. A crew that washes a lot without any of them has no answer to the permit's first question.

Washing that occurs primarily on impervious surfaces must settle the washwater, block channeled flow such as storm sewers, or direct it to soil. — Wisconsin DNR, Low-Impact Discharge general permit WI-0066575-01-0, retrieved 2026-09-29

Soap, surfactants and visible foam

Foam is a visible test. The permit says detergents in discharges to surface waters must not be present in amounts that cause visible foam beyond trace amounts.

You meet the rule one of two ways. Use only biodegradable soaps and detergents, in the minimum amount needed to clean the object. Or use only low-phosphate soaps, under 0.5 percent phosphate, or non-phosphate ones if the water goes straight to surface waters.

Dial the mix down on the job, not just in the shop. A crew that rinses a lather into an inlet has already failed the visible test.

0.5% phosphateDetergents must be biodegradable and used at the minimum amount, or be low-phosphate under 0.5 percent or non-phosphate. — Wisconsin DNR, Low-Impact Discharge general permit WI-0066575-01-0, retrieved 2026-09-29

Brighteners and acid cleaners must hold pH between 6 and 9

Any chemical brightener or cleaner has to be limited so the washwater discharge stays between pH 6.0 and 9.0, inclusive. The permit's example is hydrofluoric acid on stainless steel.

The range matters to a trade that uses strong products to lift rust, oxidation and efflorescence. An acid wash that leaves the discharge at pH 3 does not meet it.

Keep pH strips in the truck and record the reading in the log. Neutralize before the water leaves the work area, and skip the products that cannot be brought into range.

pH 6.0 to 9.0Chemical brighteners or cleaners must be limited to keep discharge pH between 6.0 and 9.0 standard units, inclusive. — Wisconsin DNR, Low-Impact Discharge general permit WI-0066575-01-0, retrieved 2026-09-29

Pick a method for each surface before you quote it

Match each job to one rule above and put the method in the quote. That keeps the customer from expecting a lot wash done with the drain open.

A roof or siding job means solids and diversion. Flatwork means settling or blocking. A fleet or equipment job may mean oil, which the exclusions page handles. And a chemical job needs a pH check.

Then finish with the job-site checklist, which puts these steps in the order a crew does them.

Washing activities shall occur on grass, soil or gravel areas to the extent possible so infiltration of washwater is maximized. — Wisconsin DNR, Low-Impact Discharge general permit WI-0066575-01-0, retrieved 2026-09-29

Questions