Thoughts on Rain Barrels

In last week’s post, What Goes In Must Come Out, I discussed using water collected in rain barrels to flush the toilet. I’ve been asked for more specifics about rain barrels and how much water would really be available.

There are a lot of resources on how to build a rain barrel. A good article is Make Your Own Rain Barrel and a useful YouTube video is Urban Survival’s, How To Make A Rain Barrel. There are specifics you will have, such as what type of barrel you use and how you will deal with the overflow. But all rain barrels need to have three plumbing features:

1. a downspout that drains the roof water into the barrel: I cut our downspout and diverted the water with a couple of downspout elbows
2. a faucet at the bottom
3. an overflow near the top: I used three-inch PVC pipe (and a downspout adapter) to channel the water back into the original downspout, which goes into the ground

How much rain water can you collect? To figure that out go to save-the-rain.com. Enter your address and a Google Earth picture of your neighborhood will come up. Zoom in on your house, click each corner of your house until the roof area is covered, then hit Finished. The following Results will be displayed:

• the area of your roof is, in square meters. (To convert to square feet multiply the square meters by 10.76.)
• the amount of rain your area receives in a year, in millimeters. (To convert to inches multiply millimeters by 0.039)
• the amount of water you could harvest, in liters. (To convert to gallons multiply by 0.264.)
• and how many times, using that water, you could flush the average toilet. They are estimating the average flush to be 6 liters (or 1.58 gallons). Our toilet tank holds 3 gallons, so I’m basing my math on that number.

At our house here in Western Washington (where rain is plentiful) our results were:

• roof area: 168.6 sq m = 1814.8 sq ft
• average annual rainfall: 1100 mm = 43.3 in
• potential rainwater harvest: 185,450 l = 48,990 gal
• toilet flushes: 16,330 (3 gal tank) [flushes per day for a year: 45]

For comparison, using the same roof area, Colorado Springs, CO (where I grew up) has an average rainfall of 19.6 inches (less than half of ours).

• potential rainwater harvest: 22,174 gal
• toilet flushes: 7,391 (3 gal tank) [flushes per day for a year: 20]

There’s a lot of water draining off your roof available for collection. These numbers are assuming you collect all the water that lands on your roof (we’re collecting from two of our four downspouts). How much you store, and how you use it, is up to you.