I collect rain water , I have series of water butts and ibc which I keep covered with black polythene to keep sun off and algae away .Transfer from tank to di with hoze lock water butt pump,been doing this for years so water bill for cleaning is nothing. I had to cut a larger circular hole in IBC to get pump into tank then fitted a plastic screw top lid to hole works a treat so I love it when it rains.Only slight down side is our tiles give off tiny red particles but by time it gets to third water butt tds is 25 . Definitely makes sense but give some thought to winter as your butts (!!) and tank can freeze ,insulate with king span or better try and build small building or if your luck. A garage based system with small heater would be best case scenario.I bought a large down pipe collector from one of big harvesting companies,can't remeber name but was £50 ish with built in filter and ability to turn water straight down drain when everything is full .