Rainwater Harvesting for Drylands and Beyond by Brad Lancaster

July 8, 2014

Hidden Toxins in Roofing Materials From Which We Harvest Water

by Brad Lancaster © 2014

One of the best ways to make sure we have clean water is to avoid polluting our air and the water in the first place. This is why I recommend using only non-toxic building products and, ideally, making sure all materials in a water-collection system are rated for potable-water quality. (This is one of the 10 Cistern-System Principles from my book, Rainwater Harvesting for Drylands and Beyond, Volume 1, 2nd Edition.)

An unhappy Brad on his roof lying upon (and pointing at) the newly discovered toxic reinforcing fabric used beneath his non-toxic elastomeric roof paint.

An unhappy Brad on his roof lying upon (and pointing at) the reinforcing fabric—newly discovered to be toxic—which he used beneath his non-toxic elastomeric roof paint.

Well, I made an oversight. Most of my roof (from which I collect my drinking water) is 26-gauge corrugated galvalume steel (which I am still happy with), but over my porch roof (on which I like to sometimes sleep and use as a terrace) I used asphalt rolled roofing which I coated with non-toxic elastomeric paint. I felt good about all this until I came upon the discovery that the reinforcing fabric used to cover the seams and prevent cracking in the roof paint between sections of the rolled roofing has the following warning:


Keep Out of Reach of Children
Do not use in drinking water or food systems.

CALIF. PROP. 65 • CHEMICAL WARNING (CALIFORNIA HEALTH AND SAFETY CODE #25249.5 ET SEQ). WARNING: This product contains chemicals known to the State of California to cause cancer, birth defects or reproductive harm. Use proper protection and adequate ventilation when using product.

Note that this warning could not be found anywhere on the product. I did not find it until I searched the product’s website (after having used the product) for the Material Safety Data Sheets and other documents that let me know what is actually in the product and/or uses of the product that are not appropriate. I should have done this before using the product, but I mistakenly assumed it was just benign fabric. Lesson learned—always do the research first and don’t make decisions based on unconfirmed assumptions.

I’ve since emailed the manufacturer of the non-toxic roof paint which I used to coat the roof and fabric to see if they knew of a non-toxic alternative reinforcing fabric. They do not, thus such a product needs to be developed—spread the word.

I am continuing to pursue non-toxic options and will post them on my Roofing page that lists non-toxic options. Options for other materials can be found on my Materials and Suppliers page. Please let me know of others I have missed.

I created these pages and this blog post so you don’t have to reinvent the information wheel, and so you can leapfrog me and my learning curve in the hopes that you’ll enable others to leapfrog you.

As for my roof, I painted extra coats of non-toxic elastomeric roof paint over the reinforcing fabric, and will repaint more often than is recommended by the paint manufacturer. I don’t know if this will keep me free of toxins—it is just my stop-gap solution as I continue to ponder the situation.

If curious, see chapter 5 of Rainwater Harvesting for Drylands and Beyond, Volume 1, 2nd Edition and my YouTube channel to see more of my system.

6 Responses to “Hidden Toxins in Roofing Materials From Which We Harvest Water”

  1. Natalie Freidberg Says:

    Hi Brad,
    When I researched roofing materials for a friend in LA (who has a rainwater system which was installed by HeyTanksLA), I was appalled to find that so many toxins were making their way into the water from shingles and other roofing materials! I’m glad (& surprised) that elastomeric is safe- but as a home performance contractor I’m also concerned about the other problem with it- it’s a vapor barrier and can easily create a condensing surface inside the roof assembly, leading to mold issues. Make sure you’ve always got enough insulation under it that warm air from inside has cooled enough by the time it reaches the bottom surface, and it should be fine 🙂
    Check out our local fave http://www.zeroimpacthome.com – he had a zero water/sewer charge bill earlier this year!

  2. Megan Says:

    Thanks for your comment, Natalie. Many elastomeric paints are toxic, as they contain biocides to inhibit growth of moss and fungi on the roof. Thus if using elastomeric paints, it is important to get a paint without biocides. See here for more. -Brad

  3. prepping – 7_10_2014 | Headline News Says:

    […] Hidden Toxins in Roofing Materials From Which We Harvest Water […]

  4. Sherrill Thomson Says:

    Thank you for this article. Back in the early 50’s my grandmother collected rain water from her asphalt shingle roof. It was a good idea I thought, except that I worried about toxins in the water from the runoff. She also used grey water from her wringer washer and rinse tubs for watering the trees. It worked well. This was on Tucson’s south side. I’m so glad you are doing so much to making good use of the precious water in Tucson. By the way, my grandmother always said that the rainwater was great for her hair when she washed it. I’m in Oregon now and my hair gets rained on plenty…..I’d say all she was doing was saving tap water, which is a good idea.
    Thank you for all you have done and are doing for Tucson. What you are doing is historic and you make one of the best differences for Tucson that we will ever see.

  5. Swen @ Gardena Rasensprenger Says:

    Rain water harvesting is good to be done but care must be taken that our roofs should be toxin free.

  6. allison Says:

    Have you heard of any issues with aluminum contamination of water collected off of galvalume roofs? Aluminum is implicated in alzheimers etc and I’m wondering if there have been any studies checking the levels of that contaminate in water saved from galvalume roofs.

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