You will definitely get some Zinc/Zinc Oxide (from the galvanizing) and Iron Oxide wash into the pond from the galvanized roofing. Hopefully someone knows whether or not these would be a problem - I tend to think not.

I would not divert runoff from a brand new galvanized roof into a pond because the roofing sheets are impregnated with something akin to "Silicon Spray" when manufactured/shipped. I believe this is done as a preservative or to keep them from sticking together in shipping; I know it makes them very slippery (have the scars to prove it). The "Silicon" stuff neithers smells nor tastes particularly healthy.

After the roof has weathered a while (several months/rains), this stuff is gone. Past that point in time, I don't think you'd have anything run off the roof (other than the zinc/iron oxides) that wouldn't get washed into the pond from any regular watershed.

"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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