2. Things you'll need: Approx. total cost $100 - $150

3. 55 gallon plastic drum. Rural King has them for $20 but you can get them free some places.
Try car washes as that's how they get their soap. (Make sure to rinse them out.)
Not a good idea to use metal drums. They rust and hard to clean.
Fruit Juice processing plants also has them.
In a pinch, Home Depot has 55 Gal Industrial Plastic Drums for $87.

4. Lengths of roof gutter for your home or carport. I used my carport.

5. 3 hangers for every 10 feet of gutter

6. A downspout fitting and length of down spout to reach the barrel.

7. Splices to connect the lengths of gutter and the down spout adapter.

8. A funnel to direct the water from the downspout into the barrel. Plan on a screen to collect debris.

9. A 3/4" spigot for a garden hose and a 3/4" bulk head fitting for the barrel itself.
(On the bulkhead fitting, the rubber washer goes inside barrel, plastic washer outside barrel.)
You'll need an appropriate size hole saw to cut hole in side of barrel near the bottom
Don't drill too close to the bottom, plan on about 5" up to the center.
They may not make an exact fit hole saw, so get the next smaller one then file the hole to fit.
Make sure to drill this hole under one of the bungs on the top of the barrel to get the bulk head fitting in.
I used a stiff metal wire from the top bung to the hole I drilled then slid the bulkhead fitting down the wire.
Drill approx. a 1" hole near the top of the barrel, in the side, to let the overflow out. .
You could even install a 1" pvc male adapter in this hole and then run 1" pvc somewhere more convenient
which is seen in the photo.
I was afraid the overflow might undermine the cement blocks.

10. Cement blocks or something else to raise the barrel off the ground a little for the hose to attach.
I used a total of 6, in pairs, so I could gravity feed water to my garden and get a bucket under it.

11. Here's a link to get you started. Lowes Gutter Systems

12. Project Complete. Will add more barrels at later date.
Current setup on my carport is 22ft X 12ft=264sq ft X .56 or 148 gallons of water per inch of rain.
The yellow funnel at the top slides into the drum bung perfect and has a screen although I added more screen.
The yellow funnel can be found in my Amazon links page.

13. The hardest and most time consuming part of the project was getting the blocks level. lol

14. The final piece of the puzzle I'm working on is a quick drain valve at the bottom of each barrel.
Using the garden hose to drain still leaves several gallons in the very bottom.

Very cool. I had just finished this project when a very brief thunderstorm rolled in. Maybe 5 minutes of rain.
55 gallon drum was already 1/4 full. This is working out perfect.
Update: 2 more brief storms and drum is now full. Rain gauge says only 1/2" of rain fell.

2nd Update: Please, no excuses about living in an HOA controlled housing project.
Most homes I've seen in these projects already have rain gutters installed.
2 options.
Install the barrels behind a decorative fence behind the house
or pre-build/design the system and store inside your garage for when you need it.
The last person you'll ever see when shtf, is the local HOA enforcer.

Total Cost to add 2nd 55 gallon drum....$56...110 gallons total renewable water storage.
You'll need two 3/4" bulk head fittings. One for each barrel. Also, (2) 3/4" pvc male adapters.
(On the bulkhead fitting, the rubber washer goes inside barrel, plastic washer outside barrel.)
The 2nd barrel is connected to the 1st with 3/4" pvc near the bottom. Same level as the spigot.
As the water level in the 1st barrel rises, the 2nd barrel fills automatically to the same level.
Drill a couple of 1/4" holes under the lip of the lid, on the 2nd barrel, to let air pressure out.
The overflow on the 1st barrel will keep the 2nd barrel from overflowing.

You could add as many barrels as you want.
The key is making sure the tops of the barrels are at the same height.

How to purify rainwater?