DIY Water Filter Activated Charcoal

[Prep Girl]

Great timing WnC been wondering how I could filter the water that goes in to the water butt that I haven't actually got yet the delay on buying one is space on my balcony.
The guttering must be broken on the roof coz when it rains it pours down onto the left side, been trying to think of the best way to catch it without taking up to much space, been toying with the idea of cementing guttering around the top of the walls then feeding it into smaller containers like 5ltr juice bottles that we use at work, was thinking I could hang them neatly round the walls and feed the water in to them but haven't quite worked out how yet.