Saving Water

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While we were in Europe, I developed a new hobby: self-sufficiency. It has led to the recent posts about cooking and shopping and what all it takes to look groomed. Some of you have laughed, but I warn you, we’re about to go swimming in the deep end.

You see, it occurred to me, while sitting on the lakeshore in Bellagio watching the fisherman pull in his nets, that with a suitable location it might be possible to retire from working and live a life that wouldn’t wear so hard on the earth. Mostly it was an intriguing thought experiment, but now with the job market being what it is and the not-too-distant sale of my house, it’s a little more practical to think about. So I’ve been reading up on sustainable living, which includes totally normal things like growing fruits and vegetables in your backyard to crazier stuff like how to farm your own fish in a tank under your tomatoes.

Yesterday, I was looking into catching and storing your own rainwater. I like the self-sufficiency of the idea, but wondered if, like most solar installations, it costs more than it saves. I did some digging and found that the average American family uses 236 gallons of water per day, or 86,447 gallons a year. I added up my own numbers and figured a family of four could get by on 138 gallons of water per day between four showers, 8 teeth brushings, cooking, running the dishwasher, a load of laundry, and five bathroom visits each. 138 gallons per day adds up to 50,370 gallons per year. Coincidentally, about 47,500 gallons of water each year falls on a 3000 sq.ft. roof in the east bay. So that’s good—with some tinkering, you could get by on the amount of rain you get—as long as you can store all the winter surplus for use in the summer.

So this is where it gets fancy. Because we have dry summers and wet winters, by the end of March, on average, you would have to be holding 19,672 gallons of water in storage to get you through to September. That’s a little more than most backyard swimming pools. Obviously, the first best step is to see how little water you could get by on each day. If you saved your laundry, shower, sink, and dishwasher water for use in the toilets and the garden, you could get by on 88 gallons per day, and you’d only need to store 16,104 gallons of water. That’s still a lot, but not impossible. Adam had mentioned seeing something the other day where people sunk massive water tanks under their driveway to store all their rainwater. Since a 5,000-gallon tank runs about $2000, and I can get no clearer indication on how much a complete system costs, I decided to guesstimate $10,000. This could be wildly off, but we’re using the guess-and-check method here. My question is: which offers the better return on investment, leaving the $10,000 invested with compound interest and paying your water bill, or buying your own water system and investing the saved the water bill payments. Like always, I gleefully trotted out my excel spreadsheet and furiously typed in my calculations.

Interestingly, buying one gallon of water in the East Bay costs the same as buying 172 gallons per day, so if you’re going to try to save here, you’ve gotta’ go whole hog. A family using our 138 gallons of water per day and living above 600 ft. in elevation (because who doesn’t want a view?) pays $918.04 per year to East Bay MUD. If that same family saved that money each year and invested it in the same interest-bearing vehicle as they would have had the $10,000 in, they save about a thousand dollars a year, while the $10,000 only makes about $300 in the early years. By buying the water system, the family starts making money in year 11. Now that’s a long time to wait for something to pay you back, but after thirty years, the water tanks are ahead by $41,336,99 (adjusted to today’s dollars). Even if you need a new pump or some filters, I still think you’re ahead. If you’re like my grandparents and you spend 55 years in your East bay house on the hill, the water tanks installed the first year in the house pay you back $199,793.60 (in today’s dollars) more than the $10,000 would.

I’m not yet saying that this is what you should do with your money or your water. There are probably a number of other hidden costs, like maintenance, energy to run the pumps, filters, etc. Let’s say it costs you $200 a year in maintenance. You’re still ahead at year 15. All that additional costs do is move your break-even date. What I’m saying is that it is a financially reasonable decision to save and filter your own rainwater. Now it’s time to look into a pond as storage that would also farm tilapia and fertilize the tomatoes.

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This page contains a single entry by published on February 26, 2009 10:30 AM.

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