Economics of the Rain Barrel

Rain barrels are the rage right now. A 55 gallon re-purposed food barrel at the downspout is one’s statement of their stance on storm water run-off and urban regeneration. Sort of like what the Prius is to gasoline consumption. Sort of.

The assumption I make of those who urban homestead is that they do it to improve regional & household ecology AND economy. I don’t want to discount those who homestead as a hobby for enjoyment & recreation but the focus of this, and most blog posts on this site, will be on ecosystem services and household economics, so let’s take a look at how the rain barrel does on these two fronts.

2 rain barrels daisy chained together

2 rain barrels daisy chained together

Economics is essentially the study of why people do one thing instead of another, the incentives that are in play and the thinking that happens at the margins of decision making. It’s not always about money. Economics gets a bad rap in that regard. It’s a tool, and like any tool it can be used in many ways. Economic theory and analysis can be used to drive a bubble of mortgage backed derivative purchases to the point of global economic crisis as easily as they can be used to empower a resurgence of localized, sustainable agriculture.

So what are some things that may motivate a person to install a rain barrel, or 2, or 3?

1. To reduce the impact of combined sewer overflow (CSO) events that occur during periods of heavy rain & run-off which deposit untreated sewage into waterways
2. To reduce demand on ground-water resources
3. To reduce the energy that’s required to obtain fresh water (i.e. energy used to pump from ground or surface reservoirs)
4. To increase resiliency during prolonged dry spells
5. To develop a deeper connection to weather and climate patterns
6. To save money on the water bill

There are undoubtedly more. I expect that many people are inspired by 1 thru 5 and that of that group some are driven to action. I will hypothesize that #6 is what tips the scales though. Let’s face it, money still matters. Accepting that there are motivators that matter besides money, but that people do want to know if their actions make financial sense, let’s look at the payback for rain barrels.

First, what is the investment? Like anything, there is variability. If you’re willing to buy the barrel and do the work yourself to add the fittings you will likely be in the $30-$45 range. I went this route, bought 55 gal. food barrels for $20 apiece, and spent about $20 more apiece on fittings. I’ve since seen barrels as low as $12 and could probably get the price on fittings down a bit now that I know exactly what works. To my amazement, I’ve seen completely fitted and plumbed rain barrels, made from re-purposed food grade barrels, for $45, before delivery or pick-up. I find that rather incredible given my DIY costs. At these prices, rainwater storage is in the ballpark of $0.60 to $1.00 per gallon. I suggest keeping the $1.00 per gallon figure in mind when shopping around for rain barrels. For simplicity’s sake in this analysis I’m going to use $50 per 55 gal. barrel as the requisite investment.

In Burlington Vermont the water bill works out to about 1.2 cents per gallon. This accounts for both water coming in, which is metered and waste water going out, which is not directly metered but is billed per the same volume as incoming. This is the price you pay at the outside tap when you fill up a watering can from city water, regardless of the fact that the water is not entering the waste water stream. For every gallon of water you use out of a rain barrel, you save 1.2 cents. If you’re on private well water supply, the economics are quite different, and are determined by the depth of your well and your energy cost for pumping that water to the surface. This is an area worth looking at, but I have not examined those numbers yet.

The next piece is the tricky part. How much rainwater do you use? Unless you count the number of watering cans you fill, there’s a big unknown here.

That’s because the amount of rainwater captured and used is a function of 3 variables:

1. How much rain water storage do you have? (1 55 gal. barrel? 10 55 gal. barrels? One 2,000 gallon cistern?)

2. How much building footprint area are you collecting from?

3. What are your rainwater use patterns? Did you empty the barrels before a big rain or not?

To collect all the rain that falls on your home, you need a barrel large enough to store the largest expected rain event. Say that is 2″ and your home has a 1,000 square foot footprint.

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You will need 1,250 gallons of storage. That’s about twenty three 55 gal. barrels. That one rain barrel at a downspout is more like 1/23rd of a Prius now. At a 1,000 sf home, one rain barrel is only collecting the first 0.09″ of rain. Everything after that is going out the overflow and on to the usual places.

Ok, so you don’t want to buy 23 rain barrels and line them up all the way around your house. That’s reasonable. Let’s say that you will buy 4 rain barrels and put 2 on either side of the house at the downspouts. From November to April you bypass the barrels completely so you don’t get 440 lb blocks of ice. In Vermont this reduces the annual precipitation you can capture from 36″ to 24″ Let’s also say that you watch the weather closely and when it’s raining frequently or there is a storm approaching, you draw the barrels down so the maximum amount of new rain fall will be captured. Let’s say that in this way you’re able to capture and use 30% of the 24″ of rain that falls on your house during the non-freezing months. The rest is overflow during the heavier rain events. This equates to 4,500 gallons. Not bad. At 1.2 cents per gallon you have saved $54 on your water bill for the year, had you used that same amount of water from the tap. I ballparked the investment at $50 per barrel, so the payback here is a little under 4 years, assuming gutters and downspouts are already in place and you are simply diverting those to the rain barrels.

For readers in the Champlain basin of Vermont, you can improve the payback on rainwater collection further. Check out incentives from the Let it Rain program for downspout disconnection, rain barrels, rain gardens, cisterns and permeable pavers offered through June 30, 2013.

Interestingly, if you maxed out storage to collect all of that 2″ deluge rain event, your investment on 23 barrels would be $1,150 and you’d collect 15,000 gallons, offsetting $180, for a payback of 6.3 years. This is about 50% longer than the 4 barrel scenario. At some point there are diminishing returns to catching every last drop. Between catching nothing and catching everything, there is a sweet spot where you use what you catch and you need what you use. If reducing peak storm water run-off and the associated ecological benefits is your primary goal, you will need to size your system large enough to catch a significant portion of that 2″ (or more) rain event. If providing water for gardens and fruit trees is the goal, you may wish to size smaller, or at least size proportionately to the water demand of your plants.

An alternative to the 55 gal. food barrel is the 275 gal. Intermediate Bulk Container (IBC). These cube shaped liquid storage tanks are sized for transport on pallets. If you’re buying re-purposed be absolutely sure to ask and verify the original contents. You do not want petroleum oils, non-organic soaps or other nasty unknowns in your water. I’ve seen this type of re-purposed tank for sale for $75-$150, which works out to about $0.30 to $0.50 per gallon of storage.

photo: Sun, Rain, Earth, A Self-Sufficiency Journey

photo: Sun, Rain, Earth, A Self-Sufficiency Journey

photo: Sun, Rain, Earth, A Self-Sufficiency Journey

photo: Sun, Rain, Earth, A Self-Sufficiency Journey

I haven’t yet gone into detail on uses of collected rain water, consideration of roofing materials, and the 3 crucial components:

1. An adequately sized overflow line

2. A first flush

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diverter to bypass the dirtiest water

3. A winter bypass to avoid frozen disasters.

My next post on rain water collection will tackle these topics.