The water goes green because sunlight is getting to it; make sure your
drainpipe goes into a lidded butt - there should be a hole ( or
perforation )
in the lid which'll allow a snug fit.
As for beasties, I suffer from the little red wriggling worms (
which
are midge larvae ), so I don't think it's easy to keep insects out - they
can
always get down the drainpipe. My suggestion is a bit of very fine net or
stocking over the end of the drainpipe, but you'll have to inspect it from
time to time to keeep it clear.

Andy.

"Jo" wrote in message
...
How can I collect rainwater without it going stagnant? My waterbutt always
goes green (the water, not the butt!) and has all sorts of nasty insects
living in it, not nice...!

Does it need to be out of the sun / lidded? Or can I add steriliser
tablets,
or something?

Any other good ideas how to collect clean rainwater for indoor houseplant
use?

Many thanks!!
(sorry if I sound ignorant, I'm a bit of a newbie)