I currently use rainwater for toilet flushing with no problem. The supply is a 1000 lt tank fed from the roof downpipe via a filtered funnel and there is no evidence of solids in the cistern or tank. Now I am shortly to add an extension to my bungalow and as plumbing will be involved I am considering using rainwater for all hot water. The general idea is to pump the rainwater to the HW storage tank with a back pressure controlled pump,via a further fine filter, and to top up the tank if necessary with mains water fed into the fill funnel. Thus there is no possibility of backfeed to the mains as there is no piped connection. Can anyone out there foresee any problems? TIA