I have basically the same setup. 8x10 shed in the back yard, three 55 drums that are kept full with water treatment. I am also in the process of installing some sort of rain catcher. But as a backup to refill my drums in case I run low. I don't want to install these "super" collectors that filter out leaves and such as I don't have any trees. I am more thinking of just installing/threading in a fitting to attach a garden hose, and block the normal down pipe with plastic and a sandbag.