I have an annoying but workable system off the house gutters - 600 (+/-) gallons in second-hand poly tanks direct-filled and plumbed together, and another 550ish on an elevated platform up the hill. Currently sump-pumping water from the house-tanks to hill-tanks (when there's enough) to get better head-pressure for the garden (and double the storage). Current use is limited to garden/yard and animals, but I'm hoping to set up a filter and plumb it into the house system at some point. The utility of that project makes it a back-burner - we're in interior Alaska, so rainwater only works from late April through late September.
