The Natural Philosopher says...
Only one caveat. Algae growth. D not havbe an anwer for that other than
a capful of bleach in the tank every week.



Possibly but not sure. The water in our other water butt is
crystal clear all the time, presumably because it has a lid
so no light gets in.

However, I've noticed on television when eco-friendly
houses are shown that the (rain-water) toilet bowls have a
distinct brown stain around them. I don't know if that is
down to the water or the owners not bleaching or otherwise
using chemicals to clean the loo.

--
David in Normandy