[permaculture] Roofing materials and water collection

Robyn Francis robyn at permaculture.com.au
Sat May 14 20:32:40 EDT 2011

The water off metal rooves is the main drinking water for most of rural
Australia, and has been for almost a century. Here at Djanbung it provides
our only supply of potable water for drinking, cooking and household use.
I've drunk rainwater from metal roofs most of my life and its my favourite
drinking water. 

The main points re roof collected rainwater water quality are
€ keeping the gutters clean
€ installing a first flush diverter to divert any dust and bird poops on the
roof away from the tank
€ Ensuring the tank is closed (no light penetration to stimulate algae
growth) and has mosquito screen on all inlets and outlets - also stops frogs
from moving into the tank

The biggest quality issue is if you live in an area with a lot of airborn
toxic pollution (agricultural spray drift, or near mining operations that
emit toxic chemicals). BTW Michael Mobbs (Sustainable House) in the heart of
Sydney city has been collecting, treating and drinking roof-collected
rainwater for the past 13 years and monitors the quality - he has a small
filtration device on a dedicated tap at the kitchen sink for drinking &


On 14/05/11 2:31 PM, "Lawrence F. London, Jr." <venaurafarm at bellsouth.net>

> On 5/13/2011 11:39 PM, Stephen Sherman wrote:
>> Thanks, appreciate the experience. Reinforces what I had heard elsewhere
>> about the longevity of the painted roofing.
>> Question still remains (in my mind at least) is it safe to drink the
>> water which comes off this painted roofing?  Would you do it on a
>> regular basis?
> There's the difference. I do not know what chemicals may diffuse from
> painted roofing into rainwater which may have a low pH. With a
> galvanized metal roof you are dealing with the galvanizing chemicals
> which may include zinc which is toxic and may diffuse into acid
> rainwater. As for fasteners it would be important not to use leadhead
> nails to attach the roofing; this goes without saying. Maybe the painted
> roofing would be safer. What about bird doo and rotted vegetation, dust
> particles of all sorts that get mixed with rainwater?
> Purchase one panel each of the 5V galvanized and one of the painted -
> mount them outside and collect water that runs off them - then have it
> tested. Also, get MSDS's (Material Safety Data Sheet) for each product
> and read what chemicals are in the paint and what the galvanizing agents
> are then do extensive Google searches for more info on potential
> toxicity from these roofing materials that might affect collected
> rainwater used for human consumption - maybe OK for washing but not food
> prep or drinking - maybe some filtering required.
> question put to Google like:
> "toxicity problems with rainwater collected off metal roofing"
> Tried that phrase and got:
> Information on Zinc Oxide in Construction - Zinc Metal Roofing Systems
> The run-off water can contain zinc ions. Since zinc is an element
> essential for life and most organisms ... For instance, rainwater
> collected from VM ZINC roofs, can be used without any known problems for
> watering plants. ... Actually there are many types of heavy metals some
> that are toxic and some that are not. ...
> www.metal-roofing-zinc.com/zinc_roofing_basics.htm - Cached - Similar
> and:
> http://www.homesteadingtoday.com/archive/index.php/t-376478.html
> Key reply:
> "I wouldn't drink rainwater off a roof unless it had been sterilized by
> some means, boiling or chlorine or such. Bird poop can carry some nasty
> parasites and pathogens. You can do it, and get away with it, but it is
> a gamble."
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Permaculture College Australia inc
Pathways to sustainability through
Accredited Permaculture Training
Certificates III & IV and Diploma of Permaculture
PDC and short courses

Robyn Francis 
International permaculture design and
sustainability consultant, educator & facilitator

Djanbung Gardens 
Permaculture Education Centre & Demonstration Farm
PO Box 379 Nimbin NSW 2480
02-6689 1755  /  0429 147 138

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