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Best Practices

FAQ: Hidden Risks of Cleaning a Paintbrush

Research seems skimpy, but think twice about washing paint brushes and rollers out in the sink

Washing a paint brush in the sink after applying water-based paint is common. Are there environmental risks associated with sending wash water down the drain? Photo courtesy Scott Gibson.

Question: A major selling point for water-based paints is that they can be cleaned up with soap and water—there’s no need for petroleum-based solvents. But what about the paint residue that’s washed down the drain? Does this represent an environmental hazard?

This question comes from Marcia Silver, a physician, who wrote to comment on an article about paint that appeared in Fine Homebuilding magazine. Although Silver found the article helpful, she added this:

“I worry about the impact of these soap-and-water clean-up products on the quality of our drinking water. What harm are these chemicals that we wash into our public wastewater streams doing to our drinking water, lakes and rivers, etc.?”

It’s a stretch to call this a “frequently asked question.” In fact, no one at GBA or FHB could remember anyone asking about this in the past. But Silver’s query struck us as both intriguing and important. According to the American Coatings Association, a trade group, roughly 700 million gallons of latex paint is sold in the U.S. annually. If only a very small fraction of that ends up in rinse water that goes down the drain, it adds up to a significant amount of paint. Is it an unrecognized environmental hazard?

There are no definitive answers

Apparently, there has been little, if any, research that would quantify the extent of this problem, if there is one. Queries to a variety of environmental and governmental groups did turn up evidence of some concern, especially in Europe, but no definitive word on whether the practice is environmentally harmful. GBA contacted the Office of Water in the Environmental Protection Agency’s Office of Science and Technology and was told there’s no current research underway on the issue.

The question also drew a blank with the paint industry itself. “I don’t think we have anything documented as an industry,” David Darling of the American Coatings Association (ACA) said in a telephone call.

In a written ACA Guide, the association says paint does not have to be treated as a hazardous waste. Still, latex paint should not be poured down the drain. As much paint as possible should removed from either brush or roller before the tools are washed in the sink. “While small amounts of latex paint can safely be washed down the drain to a septic system or wastewater treatment plant, this practice should be limited to occasional brush, roller, or applicator clean-up,” the ACA says. “Frequent disposal of latex paint rinse water can harm a septic system.”

Darling added: ” . . . washing brushes here and there—not a problem. I think the concern would be a contractor or somebody who’s doing this every day or multiple times a day. Occasionally, fine. But once you get into a regular thing, probably not a good thing.”

Some guides go so far as to recommend that the wash water used for cleanup not go down the drain at all. CEPE, the European Council of the Paint, Printing Ink, and Artist’s Colours Industry, explicitly warns against the practice, however common it might be.

“Never do such cleaning by flushing the cleaning water down the sink!,” it warns in a bulletin on the topic. The water used for cleaning should be considered “as chemical household waste,” it adds, “which should be disposed of via the waste collection center of your local community.”

Alternatively, you can wait until the water has evaporated and then throw out the container with the dried paint as household waste, CEPE said.

U.S. paint manufacturer PPG offered much the same advice. In an email, a company spokeswoman said: “PPG does not recommend washing paint brushes or application equipment in the sink, but rather filling a bucket with warm, soapy water to clean, then contacting your local environmental regulatory agency for guidance on disposal of unused product and wash water. Do not pour down a drain or storm sewer. Always refer to the proper application and disposal instructions on the paint label, aligned with industry standards.”

What are the chemical dangers?

At the heart of Silver’s question is concern about the chemical components in paint. No matter what the brand, latex paint consists of binders, pigments, and a solvent (for latex paint that’s water). Other ingredients may be added to control the growth of bacteria, prevent foaming, or make the paint easier to apply, according to this document from Greenspec in the U.K.

Labels on paint cans sold in the U.S. list the contents, although non-chemists may have a little trouble deciphering what the ingredients are. Even so, harmful ingredients will be clearly marked, says Riaz Zaman, counsel for government affairs for the ACA.

Photo of a label from a can of latex paint
If paint contains harmful chemicals, they will be listed on the label, according to the American Coatings Association. This label shows none, with the possible exception of crystalline silica, which is a respiratory hazard when particulates are airborne. Photo courtesy Scott Gibson.

“If you go to any store and pick up a paint label you’ll see extensive information about what are the hazardous components in the product, what are the proper safety precautions,” he said in a telephone call. “All of that stuff is laid out on the label.”

Biocides, those chemicals used to prevent the growth of mold in the paint, are registered with the EPA and go through a rigorous screening process, Zaman said. There’s no minimum threshold (what Zaman called a “de minimus”) for listing them on the label.

“Biocides are very clearly labeled,” he said. “There’s no de minimus threshold or anything like that with biocides. If it’s in your product, it’s going to be on the label. All of that stuff is clearly mapped out on labels.”

Later, in an email, Zaman added that trace amounts of a component that do not contribute to the “principal hazard” of the product don’t have to be listed. This includes biocides.

What about proprietary ingredients that manufacturers may wish to withhold? Labeling requirements do give paint makers some leeway there, but not when it comes to compounds that might be a health hazard, he said. “You can’t withhold the hazard or the health hazard information,” Zaman said. “That’s not a trade secret. What is a trade secret is how you formulate your product. You can withhold information about your specific formula.”

The microplastics question

Another worry are the small plastic particles found in latex paints, which can be released into the environment when paint breaks down or is sanded, during the production of paint, or when paint brushes or rollers are rinsed in the sink.

In a report released this year, the Dutch National Institute for Public Health and the Environment said microplastics are widespread in the environment and an area of growing concern. “Due to their persistence they are likely to remain in the environment long after their initial release,” researchers wrote. “Microplastics can be easily ingested by organisms and can potentially be transferred within food chains. While the effects of microplastics on the environment can currently not be assessed with a conventional quantitative risk characterisation, a case by case assessment has demonstrated the adverse effects of microplastics on biota and their persistence in the environment.”

The report estimates that 690 tons of microplastics are released into the Dutch environment annually from paint, although paint is only one of many sources of plastic particles, and paint-laden rinse water plays a minor role.

In a report on microplastics and paint, CEPE said microplastics make up less than 1% of the volume and 2% of the weight of decorative waterborne paints. Microspheres and microfibers are added to enhance paint performance in a variety of ways; leaving them out would result in more maintenance cycles because the paint wouldn’t last as long.

Does the habit of washing brushes in water add to the problem? No more than 2 or 3 tons a year from decorative coatings in Europe every year, the report says.

“As far as the microplastics go,” Zaman continued, “we generally view them as being a very minor contributor, but having said that, I do think there needs to be more research done in this area.”

As for getting rid of unwanted paint, do not pour it down the drain. Contact a local waste authority or use the ACA’s disposal program called PaintCare. It’s currently available in 11 states.


Scott Gibson is a contributing writer at Green Building Advisor and Fine Homebuilding magazine. This post was updated on June 5 to add a comment from Riaz Zaman.

9 Comments

  1. Tyler Keniston | | #1

    I wonder what waste water managers and the like would say.
    Disposing properly of anything liquid is made near impossible by an utter lack of infrastructure, outreach, and accessible information. For most (at least around where I live it would seem), 'contact your local... agency' is not all that useful when it comes to such wastes. Best idea seems to be to let it evaporate. Wonder about filters too...

  2. Jon R | | #2

    Might as well generalize and say "don't put anything poisonous down the drain". In my area, anything going down the drain ends up in the river (OK, there is some treatment). In other areas, it may go into a septic field and eventually into the ground water.

  3. AlexPoi | | #3

    Just wash your equipment in a bucket of water instead of the sink. Then you can buy some flocculant and precipitates the water to dispose of the waste water safely. I know that OutPak sells a slurry solution made just for that. No expensive infrastructure needed.

    1. Charlie Sullivan | | #4

      I couldn't find any information on the ingredients of the OutPak slurry solution.

      One little thing I do is to use up all the paint from the brush that I can painting scraps of cardboard or wood that are inevitably sitting around, or even spreading a light coat of paint on exposed framing if there's some that's conveniently accessible.

      1. AlexPoi | | #6

        It's some kind of polymer flocculant. Other companies sell them too and I think you can make your own solution pretty easily (https://www.youtube.com/watch?v=3YWW20Lxpi4). The wastewater treatment plants use the same kind of process to remove the solids from the water.

        If my house were connected to a septic field, I would not dump paint in it.

        1. Charlie Sullivan | | #9

          Interesting--ammonium sulfate and lime.

  4. Tim Janson | | #5

    In Chittenden county, Vermont it's pretty easy to drop off unused liquid paint at the local hazardous waste depot. For what's left in the paint tray or pail, I just drain it into the trash can and let it dry in the there. I don't wash rollers, those get saved in the fridge for the next day or thrown out.

    Washing brushes is where the difficulty is. I try to empty the brush as much as possible before washing. I usually wash mine in the sink, which goes into my leach field. I wonder if it would be better to do the washing with a hose/ bucket so there is a chance of the paint solution drying out and becoming solid while on the the ground surface.

    1. Expert Member
      Peter Engle | | #7

      All leach fields will eventually fail, when the soil particles become clogged with undigestible waste. While latex paint is organic, it is probably not very digestible by soil microbes. Any paint solids that flow through the system will contribute to soil clogging and limit septic life. I wouldn't put any paint in my septic system. I try not to put anything in the septic system that's not human waste.

  5. John Michelotti | | #8

    Can we add to this list monofilament that comes from string trimmers? Not to mention 2 cycle engines

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