My husband plants tomato and peppers etc each year. He plants directly under the eves of the house and the water runs off the roof with each rain storm or in the spring run off. I believe this is not good for the soil he is planting the garden in since we have an asphalt roof and I can see the debris from the roof on the soil. He says not a problem, I still have a hard time eating them without thinking I am getting some sort of poison in our systems. Suggestions?



I don't have a definitive answer but researching the OSHA website, they answered this question and I have attached the answer to your question about water catchment from roofs for vegetable gardens.

For the full article go to http://en.allexperts.com/q/Occupational-OSHA-Environmental-1417/Cisterns-water-purity.htm

Here is an excerpt from that response regarding water catchment:

Nearly all types of roofs have been - and are being - used for rainwater collection, but some are better than others.
The best roofing material for rainwater catchment is uncoated stainless steel or factory-enameled galvanized steel with a baked-enamel, certified lead-free finish. With any metal coating, ask the manufacturer whether the coating contains heavy metals (red paint used on metal often contained lead in the past). Any existing metal roof being used for a potable water catchment system should be tested for lead.
Wood shakes, concrete or clay tiles, and asphalt shingles are more likely than other materials to support the growth of mold, algae, bacteria and moss, which can potentially contaminate water supplies. Treated wood shingles may leach toxic preservatives, and asphalt shingles may leach small amounts of petroleum compounds. In addition to the health concerns, a porous or rough roof surface holds back some of the water that would otherwise make it into the cistern. Asphalt roofing has a "collection efficiency" of about 85 percent while enameled steel has a collection efficiency of more than 95 percent. With asphalt roofing, more of the rainwater stays on the roof in a typical rainstorm (i.e., the roof stays wet), though the actual percentage will depend on the duration of the storm.
(note the entire URL - http....=2050 needs to be on one line).

Painted roofs, certain wood shingles and certain asphalt shingles may impart objectionable taste or odor.

If an old roof is used as the catchment area, if it is under tree branches, if the building relies on wood heat, or if the air is too polluted, you need to be wary of elevated contaminant or toxin levels. Roofs with wood shakes, concrete or clay tiles, or asphalt shingles can support unwanted biological growth, such as mold or bacteria, that will require adequate treatment. Some materials, such as terne coating, lead solder, or treated wood, can leach unwanted toxins. (again, the entire url needs to be copied into the browser)

Posted on 21 Nov 2008

Maggie Shao
Horticulture Agent, Salt Lake County

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