Water Tanks

I have a 1000 litre IBC set up at the allotment. Mine is on a pile of rocks that I needed to dispose of and is high enough that I can get a watering can under tap. The tap I purchased from ebay as the valve that was fitted let out too much water at once.
I 'Trundled' mine into position myself but two people could easily carry one. Mine is filled from the shed roof gutter and downpipe. I also built an inverted cone on top of it to catch the watr falling on it.
With the amount of rain we had last year and another large storage butt attached to greenhouse I had an ample supply of water.

The side of my garden is bordered by the farmers stone barns. About 100ft of roof. The water when it rains is wasted as we did put guttering up but it only runs into 2 water butts. So plenty when it rains and the butts are empty all summer. 

Would 2 be over kill then? 
Has your gone green?

Strangely, now you mention it, mine hasn't gone green even though its in full sun? The water from it is chrystal clear.  Mine has been in position for four years and no problems with algae.