The Best Roofing Systems For Harvesting Rainwater

The Best Roofing Systems For Harvesting Rainwater
Harvesting Rainwater

photo credit C. Frank Starmer

If you are thinking about harvesting the rainwater that runs off of your roof, You’ve got that in common with many people in our area. It looks easy enough. You might be surprised to find, though, that you can’t simply put a bucket under your downspout and call it good. Harvesting rainwater efficiently can be a much more involved process, and using the water you collect requires care and caution – especially if you plan to drink it.

Aside from where you will store it and how you will filter it, your roof also has a major impact on the quality of your rainwater. The composition of your roofing material, as well as what accumulates on top of it, contaminates rainwater as it makes its way from the clouds to your cistern. While rainwater collected from any roof needs to be treated if you want to meet EPA’s drinking water standards or reuse guidelines, studies show that some roofs contribute to cleaner rainwater than others. Below, we’ll cover the specific effects that asphalt shingle roofs and metal roofs have on harvested rainwater.

Asphalt Shingle Roofs

Asphalt fiberglass shingles are the most commonly used roofing materials out there, so odds are this is what you’ve got to start with. A lot depends on how old the roof is. New asphalt shingles produce water with a high concentration of dissolved organic carbon (DOC), which are molecules found naturally in bodies of water. In general DOC isn’t very harmful, but when combined with Chlorine, a chemical frequently used to disinfect water, DOC produces chemicals that can cause cancer if ingested. After one year, the concentration of DOC decreases to more normal levels, however, other pollutants like particulate matter, zinc and iron increase as shingles age.

Around here, many asphalt shingles are treated with a moss killer, which will complicate rainwater harvesting. Moss treatments generally contain zinc and copper which will pollute your water.

If you have an asphalt roof that was installed before 1980, my guess is that you know just by looking at it that you should not be drinking what comes off of it. Aside from being severely deteriorated, thirty-three-plus year old shingles may contain asbestos, a toxic fiber widely known to cause mesothelioma and other cancers. Shingles made since then are asbestos free.

Metal Roofs

Water collected from galvanized metal has lower concentrations of DOC and fecal bacteria than the other roofing materials. This is an obvious advantage as it will produce water with less of the microorganism that can cause diseases in people. Galvanized metals are covered with a layer of zinc to create a zinc-iron alloy coating. This seals the metal, keeping it from rusting and introducing excessive levels of iron into your water.

The metal used by Pacific West Roofing not only has a galvanized layer 50% thicker than most, it also has a Kynar 500® finish. Kynar 500® carries a 30-year paint warranty against fading, chalking, chipping, cracking or peeling, which will keep your roof looking great and keep parts of your roof out or your water.

Residential metal roofs, just like any other roof, produce water that has varying levels of bacteria like Bacillus, Staphylococcus and others that are associated with soil. So, rainwater harvested from your home’s metal roof should always be filtered and decontaminated, especially if you drink it or use it in your home.

For a free estimate on residential metal or asphalt roofing, contact Pacific West Roofing, LLC today.

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