Got room for a big stock tank?
I’ve a 10’ diameter * 2’ tall one that holds about 125 gallons
My 50’ * 20’ section of barn roof can pretty much fill it with a one inch rain.
125 gallons would last my extended family, less than 2 weeks, but I have one of those Walmart above ground pools - holds about 4000 gallons and is filled from runoff from the roof. We have filters for several hundred gallons drinking water.
However, the pool water is needed for the garden and fruit trees in the summer, and in the long run, filters run out.
We have a well, indoor toilets, and a septic tank. I see no reason why we can’t have fresh water and flushable toilets even if SHTF - it wouldn’t take that much for hubby to set up something that we could use to pump water into several 5 gallon buckets a couple of times per week. That would means showers using a watering can and the bath tub, pour water from bucket into toilet tank for flush once or twice per day, cooking and cleaning as needed.
When the New Madrid experiences a big one, they say it could take years before electric is restored. Water, cleanliness, and sanitary bathrooms are all part of increasing one’s survival chances.
I don’t have to have lights, refrigeration, or even air conditioning, but water is a necessity, and I’m too old to be trekking to an outhouse in the dead of winter.