My rain barrel design
The downspout that supplies this barrel is fed by about 300 square feet of roof, so has the potential of about 150 gallons per inch of rainfall (allowing for some losses in the collection process). Multiply Atlanta's 30 year average annual rainfall of 50 inches by 150 gallons/inch and this one downspout has a one year potential of 7500 gallons. Similar values apply to the other downspouts where barrels could be installed. Simple arithmetic indicates that the roof could potentially receive more than 25,000 gallons of rain in a typical year. I don't have a place to put a container that large.
The initial barrel is 55 gallons. This will be doubled this year and possibly increased again later. The garden plot which this collector will provide water for is about 5 feet by 13 feet. The garden will be watered either by soaker hose or drip irrigation. 110 gallons of stored water would be adequate between rainfalls in a typical year (not this year, which is the 6th year in a row with less than normal rain). 250 gallons would be adequate, but I must first build a base that can hold 5 barrels (250 gallons * 8 lb/gallon = 2000 lb, which means the base needs to be carefully designed and built).
The barrel is food grade plastic to avoid any chemicals that might harm the plants (I doubt that the sugar and caffeine in soft drink syrup are harmful to plants).
The house has overhanging trees, so the intake screens consist of hardware cloth at an angle (so the leaves will be washed away and to keep them off the mosquito screen) plus the mosquito screen over the funnel. The mosquito screen is attached to the top of the funnel by plastic ties and caulk. The caulk ensures an insect-proof connection between the screen and the funnel. The plastic ties keep the screen tight while the caulk sets. The funnel sits in a hole cut into the top of the barrel and is sealed with caulk. Water that runs off the hardware cloth and onto the top of the barrel will drain off through the original holes in the rim.
Hose bibb and base
The base is made of six 12" x 12" pavers and three 6" x 18" pavers which raise the barrel high enough to allow connecting a hose. The hose bibb is located where the pavers meet to provide "bump" protection for it.
The overflow pipe and hose bibb are carefully threaded into just-the-right-size holes drilled and filed in the barrel and are sealed with caulk.
The barrels that are placed against the brick of the house will be painted a similar color. The barrels that will be placed behind existing shrubs will be painted green to be a closer match to the plants.
The white barrels can be painted with Krylon Fusion paint for plastics. Local sources include Hobby Lobby, AutoZone and other auto supply stores - but I've found limited color selection in the stores near me. Aubuchon Hardware has the full spectrum of Fusion colors. If you buy 4 or more cans, the price with shipping is about $1/can more than the local prices and you can get ALL the colors (PDF).
The cost breakdown per barrel is something like this:
(Advance Drum Service Mableton, GA)
90 degree tailpiece for downspout $5.00
4" to 3" adapter for intake funnel $4.50
hose bibb (faucet) $3.00
fittings for overflow pipe $1.00
2 feet 3/4" pvc pipe (no cost, left from another project, estimated $1.50)
8" x 18" piece of hardware cloth (no cost, left from previous project, estimated $0.25)
caulk (no cost, left from previous project, estimated $0.10)
12" x 12" pavers (no cost, left from previous project, 6 at estimated $1.50 = $9.00)
6" x 18" pavers (no cost, left from previous project, 3 at estimated $1.50 = $4.50)
10" circle of mosquito screen estimated $0.15
Krylon Fusion paint is probably another $5 or so per barrel.
Functionality update: 21 June 2007
We spent a week visiting the grandkids. While we were away, the National Weather Service reported over an inch of rain in the area. The first barrel is full and there are no leaks. Now to add more barrels...
Functionality update: 28 July 2007
Note that the pictures show an extra paver in each stack. The additional pavers were need because of the heavy duty hose I tested with. Since there is almost zero water pressure from the barrel, a more flexible lightweight hose is more than adequate. The barrel only needs to be 3 pavers above the ground.
I added the second barrel to this downspout using a 3/4" male pipe thread to hose adapter near the bottom of each barrel. The connection bwtween barrels is made with a washing machine hose (yet another leftover) because it has the needed female hose fittings on each end. I used a submersible pump (leftover) to transfer the water in the barrel to another barrel while drilling the hole and making the connections to the added barrel. That 50 gallons put each barrel at the half-full mark, and the 1/2" of rain the next week topped off both barrels.
I'm thinking of adding a couple more barrels at a lower level, so the overflow can be run into them. That would provide additional storage and the water in the later barrels would be cleaner because the particulate matter in the incoming water would probably have sufficient velocity to go deeper in the barrel than the level of the overflow pipe.
The barrels do provide enough pressure/volume to allow using a soaker hose. I need to do some tests to determine how many gallons/hour are delivered via the soaker hose - then set up a timer to water the garden as needed.
I chose concrete pavers instead of building a support of pressure treated wood for several reasons:
1. strength - a 55 gallon drum of water weighs about 450 pounds
2. durability - they don't need to be replaced because of weathering
3. cost - pressure treated 2x4x8 is $3 (need 3 or 4), 4x4x6 is $6.50 (need 2), 80 lb bag of concrete mix is $4.70
4. convenience - I can move the pavers to another location relatively easily. Something with its feet in concrete is MUCH harder to move.
I'll update the paint cost after the first barrel is painted.
Note that there are a number of "left from previous project" items. This house is over 30 years old and ALWAYS needs some type of maintenance.