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Old 06-07-2012, 02:37 AM
 
Location: SC
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What is the verdict for using rainwater collected from asphalt roofs in rain barrels for vegetable gardens?

I've heard and read from some it is safe enough and from others it isn't. Should I make some sort of a sand prefilter to filter out zinc or whatever the harmful particles that might be dislodged from the roof shingles by the rain water?

Right now there is just a mesh screen that filters out large debris. I also covered them with pine cones after I discovered something , I thought it might be a bird, cut a whole in the screen of one of the barrels.

In my research I've learned that cedar shake roofs are not good at all including some types of metal roofs for collecting rainwater. The best roofs seem to be natural steel or ceramic.

Any suggestions?
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Old 06-07-2012, 12:01 PM
 
Location: Backwoods of Maine
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You puzzle me, emilybh. Rainwater from ANY kind of roof is widely collected for gardens. The amount of asphalt in it would be so miniscule that it wouldn't matter at all. In fact, lots of people filter their rainwater for drinking, as we eventually will do.

There is also something called a "roof washer" which comes in several designs. Basically, it's a way to drain off the 'first flush' of rain that falls on the roof, which is what carries most of the tree sap, bird poop, and other stuff away before it lands in your cistern or barrel. You can look up different designs online. But so far as I know, gardens are the #1 thing that rainwater is collected for, and asphalt shingles are the #1 roofing material in most places. Take it from there.
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Old 06-07-2012, 12:34 PM
 
Location: SC
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Quote:
Originally Posted by Nor'Eastah View Post
You puzzle me, emilybh. Rainwater from ANY kind of roof is widely collected for gardens. The amount of asphalt in it would be so miniscule that it wouldn't matter at all. In fact, lots of people filter their rainwater for drinking, as we eventually will do.

There is also something called a "roof washer" which comes in several designs. Basically, it's a way to drain off the 'first flush' of rain that falls on the roof, which is what carries most of the tree sap, bird poop, and other stuff away before it lands in your cistern or barrel. You can look up different designs online. But so far as I know, gardens are the #1 thing that rainwater is collected for, and asphalt shingles are the #1 roofing material in most places. Take it from there.
I think they are used to collect water for FLOWER gardens and lawn - not fruit and vegetable gardens.
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Old 06-07-2012, 01:13 PM
 
Location: 125 Years Too Late...
6,715 posts, read 5,652,872 times
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Quote:
Originally Posted by Nor'Eastah View Post
You puzzle me, emilybh. Rainwater from ANY kind of roof is widely collected for gardens. The amount of asphalt in it would be so miniscule that it wouldn't matter at all. In fact, lots of people filter their rainwater for drinking, as we eventually will do.

There is also something called a "roof washer" which comes in several designs. Basically, it's a way to drain off the 'first flush' of rain that falls on the roof, which is what carries most of the tree sap, bird poop, and other stuff away before it lands in your cistern or barrel. You can look up different designs online. But so far as I know, gardens are the #1 thing that rainwater is collected for, and asphalt shingles are the #1 roofing material in most places. Take it from there.
I have several books on rainwater harvesting for both drinking and use in watering plants. Yes, you can actually design the collector from the roof so that the first bit of water from a rainstorm is drained off into a "dirty barrel" for use in watering the garden, etc, and the rest goes into the dark and largely sealed cistern for drinking, cooking, bathing, etc.

One of my aunt's in-laws lived their entire lives (in Louisiana) collecting drinking water from the roof for ALL their needs, including drinking. Both lived into their nineties.
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Old 06-07-2012, 01:21 PM
 
Location: Backwoods of Maine
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Quote:
Originally Posted by emilybh View Post
I think they are used to collect water for FLOWER gardens and lawn - not fruit and vegetable gardens.
Sorry, but the rainwater is collected for any and all garden plants, including fruits and vegetables.

What puzzled me was your assumption that there is something inherently "dirty" about rainwater, as if it has been contaminated since before it even fell from the sky. In truth, rainwater is far cleaner then most city tap water, which has been "contaminated" by chlorine and flouride.

It is true that if your roof is under some very messy trees, with a lot of sap, pollen, and bird droppings from them, you will have to screen some of the coarser debris out if you intend to filter for drinking. But if you just wish to collect the water for food gardens, then sap, pollen, leaves, and bird poop won't harm the plants, or the food that they produce. Leaves and pollen are blown over to the garden anyway. Most people want birds to visit their garden to eat some of the bugs...and the birds leave, well, poop. Just as chickens would if you let them into the garden.

But if your real concern is the material your roof is made of, that's not an issue. What are you going to do -- have your house re-roofed just to collect rainwater??? It would be cheaper to have clean water trucked in. The whole idea behind rainwater catchment is to use an otheriwse wasted resource, OR to get extra water in a drought-prone area. If all the asphalt you think came off during a rain event actually did, you'd need to replace your roof every year. Fortunately, the asphalt is pretty well stuck on there, and only a miniscule amount enters the rainwater barrel.

Probably, there are other avenues you might want to look into to water your food garden. Plain ol' rain is too pedestrian for you.
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Old 06-07-2012, 02:09 PM
 
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Quote:
Originally Posted by emilybh View Post
Any suggestions?
many people are not aware that on hawaii, rainwater catchment is a common and standard method of water collecting. On some islands and in some Districts, it is the majority method cause country water services is not available or is not the prefered way to get water.

because of this, hawaii has many governement, private and educational resources available. Its also the only place where it is not uncommon to go to the home improvement store and buy rainwater catchement parts and systems right of fthe shelf. Its also not uncommon to see a catchment water supply store between a grocery store and a clothing store. (I wouldn;t be surprised if the walmart had catchement systems).

Within the USA, Hawaii is one of the most diversed areas dealing with catchment because it deals with it ranging over 12 climate zones from rainforest to arid deserts, from snow cap mountains to flatlands covered with acid rain. They have all types of roofs including typical asphalt, tiles, wood, cement, and yes, even thatch. So there really isnlt much they don;t know.

One of the most cited reference souces is the Universtity of hawaiis colege of Tropical Agriculture which has a basic catchment introduction booklet. I noticed that although it does not specifically say NO ASPHALT ROOFING, it does mention that it is an unsuaitable roofing. It appears that the concern is how enviromental contaminents interact with the asphalt roofing similar to the warnings about metal roofing in areas of high acid rain.

You can read more about this and many other issues about catchment thorugh their info pages at www.hawaiirain.org.
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Old 06-07-2012, 02:25 PM
 
Location: Interior AK
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According to the Texas Rainwater Manual, rainwater collected from asphalt and composite shingled roofs are not appropriate for potable water collection due to the possible leaching of toxins, but it is fine for irrigation. They didn't specify whether it was fine for irrigating edible plants (vegetables).

But according to the GAF Corporation, makers of asphalt and composite shingles, "Water run-off from asphalt shingles is not approved for potable water reclamation…(including) watering of fruits and vegetables for human consumption."

General practice is to avoid watering vegetables and other edible plants, such as herbs you plan to use in cooking, with rain barrel water collected from asphalt-shingle roofs. These kinds of roofs may leach various complex hydrocarbon compounds, so most people avoid using water from asphalt-shingle roofs or flat tar roofs on plants meant for human consumption. To date there is no definitive research on the amounts and types of hydrocarbon compounds which may leach from such roofs, though it is common practice to use water collected from asphalt-shingle roofs for watering ornamental plants and shrubs. Enameled steel and glazed tile roofs generate little or no contamination and rainwater harvested from them is commonly used to water vegetables

So, the lawyers say "No"... because of the possibility of leaching toxins.

However, numerous studies have shown that the primary concentration of debris, pathogens and toxins from any roof and the environment are contained in the first flush off the roof when the rain starts, a roof washer system that collects and discards the first flush separately reduces any possible toxins in the remaining water to minimal levels.

The "dirty" first flush water can be used to irrigate non-edible ornamentals, edible fruiting trees, and other non-potable household purposes. The remaining water can then be used to water edible plants such as garden vegetables, ground and vine/shrub fruits, edible flowers and herbs with no additional filtering because the minimal amount of contaminates that may remain in the water from the asphalt/composite will be filtered by the soil and the plant roots before reaching the edible portions of the plant.

If you're concerned about possible toxin build up in the soil of your garden or are extra cautious, you can pre-filter the rainwater through a sand or charcoal filter, or restrict usage to only vegetables and fruits that the edible portion is not in direct contact with the soil (i.e. for tomatoes & peas, but not carrots and potatoes).

Note that this is the same advice given for the use of reclaimed greywater in the garden.

Rainwater from cedar shake roofs are not recommended for irrigation, especially not edible plants, for a two reasons. 1) Cedar has natural chemical properties that retard the growth of other plants and beneficial soil bacteria and organisms (which is why we build with it!); 2) Cedar shakes are often further treated with additional fungicides and preservatives (like copper, zinc & arsenic) that can be harmful to soil, plants and humans when concentrated (which is why we don't use treated lumber for garden beds). First flush roof washers have not been shown to entirely remove the natural cedar compounds.

In some metal roofs and gutters, the materials to weld/solder or caulk/seal the seams may contain hazardous materials... such as lead or toxic hydrocarbons. Some galvanized roofs may also leach small amounts of zinc, but this is normally well within safe limits (zinc is not toxic to soil, plants or humans in normal concentrations). Caution should be used with rain collected from copper roofs and gutters, and roofs that contain copper anti-moss strips/treatments because copper is a natural fungicide and antibacterial which is harmful to the beneficial soil bacteria and organisms. But, again, a first flush roof washer system should be adequate reduce these risks to acceptable levels for irrigation of edible and non-edible gardens and orchards.

FWIW, we had rainwater from our asphalt shingle roof tested and it didn't show any abnormal concentrations of environmental toxins or biological pathogens.
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Old 06-07-2012, 02:44 PM
 
Location: Somewhere in northern Alabama
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Rainwater (and snow) can be dirty, even though much of it is pretty clean. The core of snowdrops and rain is often bacteria or pollen. On a more coarse scale, there is one season in Florida where the winds come from the Sahara, across the Atlantic, and deposit dirt and sand from dust storms in the rainfall that washes the air. I experienced this first hand because the stuff had to be cleaned out of our pool.

A neighbor got a lesson with dirty falling snow here. The family had been unused to large snowfalls, and the winter before last when one occurred, the kids and a parent went out collecting snowflakes on the tongue. In three days, all of them were sick and the ones who avoided it were fine.

I'm not a fan of flouride, and am glad to be away from that. Chlorine is much much more common and every grain of salt has a chlorine end to it.
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Old 06-07-2012, 03:08 PM
 
Location: Interior AK
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According to this USGS study, and a few others from Germany, the majority of toxins found in rainwater roof run-off from both asphalt and metal roofs were environmental contaminates DEPOSITED on the roof and not from the roofing material itself.

The Center for Rainwater Harvesting compiled a table from all available research done on various roofing materials and the contaminants found in rainwater collected from them. However, this information is inconclusive because there is no standardization across the testing methods -- time of sampling during the rainfall, from different locations in the system, and the units of measure.

There is a list of reference links at the bottom of the table if you want to read each of the studies yourself and make your own conclusions. Of interest is the Newcastle NSW study that indicated rainwater coming off a DIRTY roof and gutter system contained only higher-than-limit fecal coliforms --- which certainly shouldn't be a huge concern for a garden since it's still lower than what is in the soil itself already.
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Old 06-07-2012, 06:39 PM
 
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I would be concerned about asphalt roofing if it were a newer roof and in very warm weather where the tars may be more volatile. Again, it's a first flush issue like others have said.

We have a large cistern (8000 gallons) collected from a 10-15 y/o asphalt roof on our house. We will be using the water for lawns, trees and ornamentals to keep the water bill down. The plan is to put another cistern in to collect rain from the garage that will be used in the same way. When we build our barn it will have a metal roof and a large cistern for the vegetable garden and the plan for that system is a fairly large water tower for pressure and storage. When it comes time to re-roof anything, we will use metal not only for the cistern but for hail resistance. Our last water plan is a small covered swimming pool for both summer cooling but in a pinch for bathing, washing clothes and filtering for drinking at the house.

Another good and informative thread.
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