For the price of a 55 gallon plastic barrel (sometimes free), and about $10 in parts, you can build your own rainwater collection system. Water is good. Free water is better.
If you already know that water won't run uphill and how to handle a drill, you can do this. The most ingenious part of the design is the hose-to-barrel connection. Since the attached hose will frequently be tugged during normal use, it is important to use a mechanical connection rather than a glued connection.
This design uses a simple garden hose washer, standard garden hose parts, and a special adapter, that's not really all that special. It's expandable and useful for more than just capturing rain water.
Step 1: Got Parts?
You will need a barrel. The bigger the better. 55 gallon is good. I like plastic, but metal will work. Don't use barrels that held something toxic in a former life, go for something wholesome, like lawn fertilizer, or laundry detergent. I picked up this one at a local recycler for $4.
Also, while in town, pick up a garden hose valve, garden hose washer, and a MHT to FPT 3/4" plastic adapter. What? MHT = Male Hose Thread. FPT = Female Pipe Thread. Plastic = plastic. You'll know it when you see it. Less than $10 total.
I had some old parts handy to draw from.
The gutter modification comes later.
Step 2: Tools Needed
A drill. 1" drill bit. A Keyhole saw. That's all you need to modify the barrel.
To modify a gutter downspout, you will also need a heavy duty pair of scissors (or sheet metal snips), about 10 small sheet metal screws, and a small drill bit to pre-drill for the screws. A pop-rivetor would also work. The special pliers shown in the photo are for "shrinking" sheet metal. Optional.
Step 3: Saw an Opening in the Top of the Barrel
Just like in the photo. Unless you want to put the opening off-center. That may work better.
Step 4: Attach Garden Hose Valve
Drill a 1" hole near the bottom of the barrel. The adapter and washer go on the inside of the barrel. The valve goes on the outside. The toughest part of this is that it requires someone with a really long arm to hold the adapter while someone else screws on the hose valve.
Step 5: Modify the Downspout
Downspouts are easy to modify. Look at one closely, it will be apparent how they fit together. Use the small drill bit to drill out existing rivets if necessary. Some are put together with sheet metal screws. Just be flexible with your tools and mind, and you will be able to build a downspout to direct rainwater into your barrel.
The parts photo shows a flexible plastic downspout that may also work.
Step 6: Add More Barrels
I added a secondary barrel using a garden hose Y adapter as shown in the photo. I modified it later to replace the Y adapter with an additional dedicated hose to fill the secondary barrel. Putting your hose connections near the bottom of the barrel allows most of the water to be utilized from all barrels, even the secondary ones.
I learned that one 55 gallon barrel can fill up in about 10 minutes of heavy rain. The secondary barrel would only partially fill in that time due to the relatively small diameter of the garden hose. Adding two or three or more secondary barrels, each with its own dedicated fill hose from the main barrel, will work much better, saving more water during those times of heavy downpour.
Make your hose-barrel connections the same way for secondary barrels. The second photo shows a cut-away mock-up of the hose-barrel connection. In this case, a quick-release brass connector just happened to work for the inside job. However, the MHT to FPT adapter is better since it has a larger diameter. A different garden hose valve did duty for the outside job.
Step 7: Enjoy Free Water!
Here's a photo of the rain barrel receiving its first deluge of rain water. There's a piece of window screen on the top of the barrel to filter out debris. The screen is also important in preventing mosquitos from entering and mulitplying.
As a bonus, this system makes a splendid watering system for gardens during dry seasons. I use tap water to fill the barrel with 15 or 20 gallons, and then use the barrel outlet hose to meter out water to specific garden areas. You can walk away from it, and your garden will slowly receive that 15 or 20 gallons, no more, no less. Very nice for those times when rain water is in short supply.