Saving Money with Rain Catchment Barrels: Doing The Math

14458354548_b5f423512d_zPrepare yourselves: this post contains math.  (Ack, the horror!)

In case you were wondering, it’s been balls hot in Texas lately.  As such, our garden is feeling the effects.  We’re having to fill the resevoir in the raised bed daily, and our in-ground roses, begonias, salvia, and snapdragon at least every other day.

Which means, we’re using somewhere in the neighborhood of 75 gallons a day to water our plants at the moment

(For those that are interested in the math – we have an approximately 8’x4’x2′ reservoir in our raised bed garden, but it’s filled with rocks.  Assuming that the actual portion that the water fills is about 1/4 of the reservoir, then, 8 cubic feet of water.  8 cubic feet is about 60 gallons.  Assuming I use about half as much again to water the in-ground plants (but that I only do it every other day) then that averages out to about 15 additional gallons a day.)

It’s that hot in Texas from about July – September.  The rest of the year, we water once or twice a week, so even taking the lower once-a week figure, that’s roughly 10k gallons a year just going directly into our flowers & veggies. Considering that our water rate (given our other residential uses – laundry, showers, cooking, etc.) is roughly $7.48 per thousand gallons used, that comes out to around $75 a year.

For water. That we’re putting right back onto the ground.

So what’s an aspiring gardener to do? Our answer: rainwater collection barrels.

We found 50-gallon barrels on Woot for $69.99 a piece.  Given that Texas (and some other states) exclude sales tax for rainwater collection, and our city subsidizes the purchase of rain barrels to the tune of 50 cents per gallon, that means we were able to purchase two barrels (or 100 gallons capacity) for just $90 total – a pretty good price.

According to stats that I found online, Austin averages between 25-40 days a year of precipitation.  Meaning our new rain barrels could help us save up to 4,000 gallons of city water, or approximately $30, a year. In other words, our rain barrels will pay for themselves in three years time, and after that, they’ll start making us money.

But wait, you say. Even if it rains 40 days a year, that doesn’t mean you’ll fill your barrels with every storm.  And that’s true, BUT…the genius of rain catchment systems is that they use the large surface area of your roof to funnel water into your barrels.  The conventional formula is that 1,000 square feet of roof + 1 inch of rain will yield you approximately 623 gallons of water.

I’m not entirely sure of our roof size, but it’s probably fairly close to 1,000 square feet.  Which means that I only need 1/6 of an inch of rain to fill our barrels.  I’m liking our chances.

So if you really want to grow your own vegetables and have it be economical, it’s basically a no-brainer. But beyond that, it’s also environmentally friendly (especially in drought-prone areas) and in an emergency situation, they can even serve as backup water for you and your family (so long as you boil it first). Win-win.

Do you use rain barrels?  Tell us your experience in the comments!  Header image courtesy of Flickr user mwms1916, under a Creative Commons license.