Hi, Sorry for the slow response. It is possible to do what you describe, but to make it work well (and putting all legalities aside- that would never be allowed in the US in a DIY system) it would be costly and require too much maintenance for it to be practical. I would encourage you to use greywater for irrigation, or if there is no irrigation potential, then nonpotable uses like toilet flushing. Rainwater is much better suited to be used for indoor use.