Put some nylon netting folded over at the top of the downpipe to catch the big bits. Tie another piece around the pipe going into the water butt. Then put some more over the submersible pump when you pump the water out before it goes through the resin. Rinse the pieces of nylon once a month to get rid of any bits that get caught. Saves loads on resin and water bills. I've had no complaints from customers in the 4 yrs I've been using rainwater. In fact ones who complain about the amount of water used are happy once I tell them I collect rainwater instead of using tapwater. Just make sure you tell them the resin costs a lot of money or they think it's costing you nothing!