toxic runoff from roof to rain barels

I was looking around and found that of the research that has been done when it comes to rain barrels and other catchments that the water coming off the roof is dangerous. Many roofs are asphalt which are loaded with tar, zinc, and anti fungal agents. For metal roofs, the galvanized kind are prone to release of the heavy metal zinc. These can be mitigated by the first flush diverts, but they are still present. I am sure to that these will release most of the particles in the first year or so, but still, it is kinda scary.

Are there any roof types that allow for water capture and don't leach dangerous carcinogens?

There's an old saying: The solution to pollution is dilution.

Once the roof has been washed by the rain for a while it won't leach much. Otherwise the roof would wash away. Roofs last 20 to 200 years. Not much leaching going on once they're established.

Now, if you want to worry about something consider what the factories and other smog producers up wind of you are pumping into the air. That gets washed out by the rain. There's you're problem.

I would think that a green roof made with a high grade pond liner has far less gick to spread to the water. The plants and soil would filter out quite a bit of air polutants. Some plants are known to take up heavy metals, so they could be removed from time to time. Probably the worst type of roof would be terne which has a lead coating instead of zink.

I've always been suspicious of using roof water for growing food because of these problem. Roofs also have lead and aluminum flashing, caulking and they get hot and gas off and do do for their entire life span and they are repositories for air pollution that gets washed off in the rain. There may be a water filter for this purpose. I hope so but until such time as one is offered I wouldn't use rain water off the roof for growing food or drinking.

Aluminum shingles from cans.
This reduces the waste stream.

Ceramic tile aka spanish tile
You'll have to do your research on the materials used in fabrication

Micro Concrete Roofing Tiles
here's a video
You can make them yourself.

Thatch
This can be done with organic material and has the advantage of being compostable when its time to replace it.

Glass
Consider covering the roof with solar thermal and PV panels

All NZers I know who collect roof water have galvanised iron. I don't collect water yet, but I will one day...from my 1950s asbestos roof.
As long as I don't inhale

it would be relatively easy to run the water through a reed bed or small constructed wetland before using it. a slow sand filter would also do the trick quite well, though they need a relatively steady flow of water to keep filtering properly. that's assuming you're stuck with a roof with nasties in it.

zinc is a desired nutrient out here. most soils will benefit from it.

Aluminum will not oxidize any more than once. it oxidizes instantly in air. thats why you can't solder it.

seems like you you get lots of yeasts and bacterias up there too.

I think galvanised iron and what we call coloursteel here (colour is bonded into the metal) is pretty low in zinc runoff in terms of drinking water or watering your garden. Where it becomes a problem is where you have alot of houses whose runoff goes into waterways. It's the accumulation from mass runoff that creates pollution, not collecting water off one roof.

Like Leila, I know lots of people who collect water off metal roofs. The issues here are to make sure there is no lead - either in paint or leaf head roofing nails if it is old, or in flashings.

"The solution to pollution is dilution"

I like that! Also, pollution is relative. I'll take water from a galv roof before mains supply water that has fluoride added and has been chlorinated.

I understand the concerns expressed but on balance a roof with diverters is effective and for my main home it is our only source of water to the cistern. The roofs is concrete and we do paint with lime wash, well after major hurricanes that strip paint, so maybe that does help. We just filter water to drink without problems, so far. After being closed up for some time there is a black algae that makes first few days showers interesting, think squid ink water, but after that all is well.
I too am more concerned with what is in the air the water falls through vs contact surface in my personal triage of safety. I know my rain came from winds that last say land fall in the Sahara.

When you hear the word 'galvanized', interpret it to mean 'zinc plated'. Galvanizing refers to the process which plates the zinc.
Before you get too concerned over water from a galvanized roof, stop and think...the city water, and your house water is most likely running through galvanized pipes to get to your faucet. The bird droppings should be a bigger concern than the zinc.

John Polk wrote:When you hear the word 'galvanized', interpret it to mean 'zinc plated'. Galvanizing refers to the process which plates the zinc.
Before you get too concerned over water from a galvanized roof, stop and think...the city water, and your house water is most likely running through galvanized pipes to get to your faucet. The bird droppings should be a bigger concern than the zinc.

lead is added to the zinc in some galvanizing processes. I would imagine that would be discouraged for galvanized water pipes, but I don't know about galvanized roofing.

I know that this is a recent reply to an old thread, but it still seems relevant.  One easy solution to the challenge of cleaning roof runoff (toxic or not) is to have the downspout empty into a rain barrel full of good quality biochar to filter the Water at the source before it is applied, then it can be attached to a hose at the bottom for cleaned Water to use in your garden. One such rain barrel I saw had collected a fist size chunk of zinc.

Eliza,

That is a great idea, thank you.