[mdjlucan]

When I was watering my vegetables and plants tonight I noticed the water was green the water has been in the sun has done this. Will this hurt the plants and vegetables thanks.

[Baldy]

Ive not heard of algae in water butts being a problem for plants - I think they'll be ok.
Might be a bit smelly though... 
I'm not a certified agribiochemist though...

Pip pip,
Balders

[Madame Cholet]

it doesn't seem to hurt mine

[Growster...]

The water in our IBCs often goes bright green, but there are no side effects!

I wouldn't worry, it may even be beneficial, but like Balders, I'm not an acrobatist!