Water butt

I have for many years had a water butt filled from the house roof.
However this year I decided to move it and collect the water from the conservatory roof.
Since doing this every thing I have watered from the butt has died but plants watered from a tap are ok.
I cleaned the butt out before using it this year as usual could it be that there is some chemical being mixed with the rain water from the self cleaning glass on the conservatory roof ?

 

I went to Germany on business about importing the self cleaning & water repelant technologies. The stuff is based on nanotechnology & didn't live up to their claims that its both water repelant and microporus. Its very new technology & to be honest, I didn't think enough research had been done on it.

That aside, was any copper used on the roof or any biocides to clean lichens off when the roof was done ?