How can I collect rainwater without it going stagnant? My waterbutt
always goes green

It only goes green if there is light getting to it. Ours has a lid but
with holes the water stays fresh and not mozzie larvae ridden. But the
latter might be due to our location rather than anything else.

I put a large, shallow terracotta bowl (with drainage holes) on top of mine,
with the base of the bowl going down towards the water. My cats love
sleeping in this in the summer as the evaporating water keeps it nice and
cool. :-)

- h