How can we safely use rainwater collected off an asphalt shingle roof?

I have a ranch style Texas house, large roof, from which I'm harvesting less than half the water and use it for pressure washing and other misc uses. Black spooge and sand from the shingles accumulates in the reservoir. The back half of house has even more area but I'm reluctant to collect that water for fish tank, chickens, and gardening.

We also have metal roofs and I harvest that in other tanks for cattle. It's much cleaner. We are on grid at this time with only genset backup so far. We also have well water.

I use rainwater from asphalt-shingle roof for watering my garden.  I do not notice shingle detritus in mine though; are your shingles very new or very old, maybe?  Also, my water barrels have screen at top intake and the outlet/tap is about 1.5 inches above the bottom of the barrel.

using that water for animals, either fish or chickens, doesn’t seem like that good an idea to me. the data i remember (from quite a while ago) was that it wasn’t remotely safe for human consumption. probably isn’t too good for chickens either.

Mk Neal wrote:I use rainwater from asphalt-shingle roof for watering my garden.  I do not notice shingle detritus in mine though; are your shingles very new or very old, maybe?  Also, my water barrels have screen at top intake and the outlet/tap is about 1.5 inches above the bottom of the barrel.

About the same here, I have a leaf screen on top, and the outlets are above the bottom. We spot the spooge when we clean the tank every year or so. It's a solid half inch on the bottom

This is a quote from the Texas Manual On Rainwater Harvesting:


"Composite or asphalt shingle Due to leaching of toxins, composite shingles are not appropriate for potable

systems, but can be used to collect water for irrigation. Composite roofs have an approximated 10-percent loss due to

inefficient flow or evaporation (Radlet and Radlet, 2004)."

Your comment about the accumulation of roof debris in the tank makes me think that water is steeped with that stuff, as it sits waiting to be used. I'd try to keep it out of the tank in the first place.
There are "first flush diverters" that dispose of the first amount of water to hit the roof in a rain. Presumably the roof debris, leaves, bird poop, and bugs get washed off the roof and dumped, and after that, the cleaner water goes to your tank.

Or you could put some sort of filter, like a radial flow filter or a slow sand filter to capture the debris and leave you with "cleaner" water. It will still have leachate from the asphalt, but not so many particles soaking in the water all year.

Do you use well water for toilet flushing? maybe this is another use for the roof water? Not sure if code technically would allow for you to plumb rainwater to the toilet (to protect your drinking water), but a flush with a pail (especially easy for #1) gets around that issue.

We use water off asphalt shingled roofs for irrigation. Our well water has too much dissolved solids (salts etc.) to keep tomatoes and squash and strawberries happy.

I've never had a sense of a problem. For example, I would expect to see a hydrocarbon sheen on the top of the water barrels -- and never have. When we had some new shingling done, though, we let the initial water after some good summer heat and rainstorms drain into non-food and shelterbelt trees. It seemed a sensible precaution.

Kenneth Elwell wrote:Your comment about the accumulation of roof debris in the tank makes me think that water is steeped with that stuff, as it sits waiting to be used. I'd try to keep it out of the tank in the first place.
There are "first flush diverters" that dispose of the first amount of water to hit the roof in a rain. Presumably the roof debris, leaves, bird poop, and bugs get washed off the roof and dumped, and after that, the cleaner water goes to your tank.

Or you could put some sort of filter, like a radial flow filter or a slow sand filter to capture the debris and leave you with "cleaner" water. It will still have leachate from the asphalt, but not so many particles soaking in the water all year.

Do you use well water for toilet flushing? maybe this is another use for the roof water? Not sure if code technically would allow for you to plumb rainwater to the toilet (to protect your drinking water), but a flush with a pail (especially easy for #1) gets around that issue.

That was the first system I built, right off the gutter into tall ex-molasses tanks that just happened to be the right height, and I didn't do first pass on it. Yep that explains some of the issue. Yes it is steeping and the spooge is surely asphalt particles that fall to the bottom. I was giving some to the chickens but have since switched them to well water. We don't have a shortage of that, I just finished building 2500g above-ground storage.

Flushing toilets with roof water is a great idea and we have no code out here in rural Texas. But this house was already built and plumbed 12 years ago, and the builder passed away, so as I have no Ouiji Board I can't ask him for details. Wish I could...locals say he was a great guy, I think he was going permie/hugel based on irrigation I discovered that he'd started in a field.  But he started working as an Exterminator then came down with cancer 7 years later. Imagine that. His twin brother is as fit as a fiddle, works as a machinist.

Douglas Alpenstock wrote:We use water off asphalt shingled roofs for irrigation. Our well water has too much dissolved solids (salts etc.) to keep tomatoes and squash and strawberries happy.

I've never had a sense of a problem. For example, I would expect to see a hydrocarbon sheen on the top of the water barrels -- and never have. When we had some new shingling done, though, we let the initial water after some good summer heat and rainstorms drain into non-food and shelterbelt trees. It seemed a sensible precaution.

I don't see a hydrocarbon sheen either. I see are you in Canadian prairies? Do you have much summer heat, as we do in Texas? That probably causes more issues by softening the asphalt.  

We have limestone water all around here in Central Texas, and other than high PH I'm not aware of it having negative effects on the garden. We do use rainwater for hand watering.

We certainly don't see Texas heat, but we will see stretches of summer weather in the 30-35C zone with long days of full sun. Enough, I hope, to cook off the bulk of the volatiles that are the biggest worry from a health perspective.

I respect that there are concerns regarding this, and some hard data from actual sampling would be of great interest. I lean toward the view that it's the dose that matters most. How would it compare to driving on a paved road in summer or filling up at a gas station?

FWIW, if I could have convinced DW I would have been inclined toward metal.

I currently capture water for my chickens from a simple tarp, filtering it through a bucket full of sand set into the top of a 55 gallon barrel.
I wonder if there is a filter that could capture the hydrocarbons?
A Solvia style vermiculture filter perhaps?
An oyster mushroom and woodchip  filter?
An IBC tote filled with wood chips, worms and mushrooms could do the trick.
I'd want to test the water before giving it tithe chickens,  but I think it could work.

William, that's a wonderful perspective on the problem -- it never even occurred to me to build a living filter. Very true, hydrocarbons are biodegradeable in small amounts and in the right conditions. This has possibilities -- thanks!

Suggest try testing the water.  Older roofs should be losing very little dangerous.  Most of the volatiles should have washed away or evaporated over time.   So risk should be small.  That said can you collect it and then do some sort of solar still?  You might still gather volatiles but a bit of fraction distillation wasting some water would likely get rid of them.  Or alternately what about reverse osmosis with the water?

C. Letellier wrote:Suggest try testing the water.  Older roofs should be losing very little dangerous.  Most of the volatiles should have washed away or evaporated over time.   So risk should be small.

I'm curious, what exactly would you test for? It seems to me that if you take a sample to a lab, you have to be pretty specific unless you have money to burn on a shotgun approach. Basically you'd be looking for a "gotcha" chemical that indicates widespread trouble. Suggestions?

This has turned into an informative thread.  Thanks to all who contributed. I marked the chicken water tank as well water only.

I'd like to do a Spirko-style above-ground 8' stock tank fish pond, just uphill from our garden.  I wonder if the roof water would be OK for that?  Our roof is 12 years old now, so much of the hydrocarbon toxins must have baked and leached out in our hot Texas summers and heavy downpours. When this roof fails, we'll go to metal, with an eye towards protecting us from 5G satellites too.