I found these barrels for sale on Craigslist for $15 apiece. They are 55 gallons, food-grade plastic, and were used to store a food preservative. The have bung-holes in the top with threaded caps so it was easy to just stick a hose in there and rinse them out. I drilled a hole about 3" from the bottom of one and installed a $2.50 outdoor faucet and sealed it with silicone. I then cut off the bottom part of my rain gutter downspout and installed an elbow to divert the water to the top of the barrel. You can buy attachments that fit onto your downspout and thread into the bung-hole, but all I did was to cover the bung-hole with some fine wire mesh from a broken window screen to keep debris and bugs out of the barrel. The water just drains right into the hole. The last step was to drill a hole about 1" from the top and install a piece of PVC pipe with a 90 degree elbow and a downpipe to act as an overflow valve. Once the barrel fills up, the excess water simply drains into the downspout pipe. You could also allow the water to drain into additional barrel(s) as long as the last one in the series is sitting at the lowest level and has its own pipe that drains into your home's downspout opening. The yield will vary according to roof size and rainfall amount. I have a pretty big roof and on a day with 1" of rain I can fill the entire barrel. I only have one installed so far but I could do 3 or 4 of them if I chose to. In a SHTF situation where the water gets shut off, I have 55 gallons of water for washing or flushing the toilet. I am sure that it is safe to drink, but I would boil it first anyway if I needed to drink it. Its easy to focus on the fun stuff like guns and ammo and camping equipment, but you cant overlook the basics like water.