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Letter Re: Concerns About Toxicity in Water From Roof Catchment Rainwater
Mr. Rawles,
I searched the forums to no avail on this topic. In the Pacific Northwest,
a common roof setup is untreated wood shakes with copper ridge caps and flashing.
The rain hits the copper which leaches chemicals onto the wood shakes to inhibit
moss growth.
On other sites I'm reading conflicting thoughts on whether this amount of
copper renders the water unsuitable for rain catchment into a water barrel
for vegetable garden irrigation or a cistern for human consumption. Some folks
seem
to think there is more danger from the concentrated nitrogen in the water (bird
droppings, raccoon feces) than the minute traces of copper. Others believe
any amount of copper renders the water useless, no matter what purification
steps
one might take (filters, Aerobic 07, etc). - What is your take? - Scott J
JWR Replies: The copper itself is not the issue, since after
all most residential water pipes are copper. But if lead solder was used for
any
joints,
that would be
cause for concern.
Personally, I'd be much more concerned about any wood preservative treatment
chemicals impregnated in the shingles. Some of those chemicals, such as copper
naphthalate,
are nasty!
But
if your roof was built with plain, untreated cedar shingles and copper sheeting
without lead joints, then the catchment water should be fine for domestic use,
once it is properly
filtered
and treated
for microbes.
