yes, you will likely get some heat for your perspective but I personally think it is an GREAT example of how to put in pencil and paper (or maybe just the ipad) th exact cost/benefits of some of these "save the earth gizmos". So...thank you.
Your next mission, should you decide to accept, is to write a similar article about the fancy composters and the related additives to speed up decaying, which BTW, cost 10 times as much as the contents of a compost bin. (!)
again, thanks for yor practical approach on the subject.
You forgot to mention the basic flaw with collecting rain water in the first place - when it goes weeks without raining, your rain barrel full of water only lasts about a week, then you're stuck using tap water until the next rain anyway. Rain barrels only stay full when you really don't need the water. I can't figure how to factor this into your calculations of cost savings, but here in Florida it's a big deal. Our water is expensive, and in short supply.
In our hot, dry spring and fall, it goes without raining routinely for 5 or 6 weeks at a time. I have four 75gal. rain barrels that run out in about 10 days if I only use their water for watering my orchids and potted plants. Luckily we also have two 600gal. cisterns that we put in behind our new shop building, and they are used exclusively on our veggie-growing bed, and earth boxes. So they last about a month with frugal use.
My philosophy on rain barrels? Go big or go home! The cisterns cost less than $400 each including delivery. Using your basic math, at $900 for 1200gal. that would equal a cost of 75cents per gallon saved versus your $3 per gallon saved. Computes out to only 2 1/2 years to pay back the cost of the cisterns. We're almost there already.
Btw, our County Extension holds rain barrel seminars each month, and sells 55gal. barrels after the class for $37.
I crossposted- didn't see yours till I had just sent mine.
You make an excellent point. That is the other end of the whole rain barrel question, and I couldn't ge into it wihtout making the article much longer. I couldn't say it any better than you did. Thanks for posting.