Hi all, First post here and hoping you can help

Would anyone like to share their plans for an off grid rainwater water system for their caravan/other dwelling? This would include hot water too. What are the options? I would rather not need to use electricity but if it could be integrated with a typical caravan's plumbing (inc. 12v submersible pump) so it would run off the caravan's battery that would be fine. Looking at wood fired or gas. let me know how you do it! Pictures are good too :-)
Many thanks for your help