Calculating the Savings of a Dual-Flush Toilet

We've been trying to figure out whether it makes economic sense to replace an old 1.6 gallon per flush toilet that needs repair with a nifty new dual flush model. Given the drought here in California, and our desire to divert water to our lawn, we were curious to find out if it would make sense. It was almost as difficult as the problem above...

Here's the quick answer: no. If you want to check our work, we downloaded a handy Excel spreadsheet from Caroma's website; did some Google bombing to find the local utility's water rates, brushed up on our basic algebra to convert their rate (a stepped rate per 100 cubic feet) to the rate the Caroma worksheet wanted (a flat rate per 100 gallons—tricky!) and shopped around for the best price we could find on a Caroma Tasman 270. We're exhausted just thinking about it again. Someone at Google: can't this be automated?

Our annual savings, according to the worksheet? $6.

That's right, $6.

But what's really surprising, especially if you've priced bottled water at the supermarket, is that $6 translates into 14,742 gallons of water saved. With economics like these, it's easy to see why Northern Californians haven't reduced their usage of water enough.

image by djayo via sxc.hu

Comments (2)

Municipal water is surprisingly cheap. I'm not sure if the amount of water you use affects what you are charged for sewer and water handling and all those other charges that show up on the utility bill. That could change the savings some if less water usage equaled lower sewer charges.

I bought my dual flow toilet because I needed to replace one toilet in the house (it was an original 1925 classic but I couldn't get a modern ball flapper to seal correctly) and it was about saving water not money. I think I only pay $3 a month in actual water usage fees. and $40 in other water related fees.

posted by ryanmarie on June 25th 2008 at 12:20pm
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I agree with ryanmarie; it's about what you're trying to save.

We're having a house built, and we decided to get dual-flush toilets in it instead of the regular kind. It counted as an "upgrade" and added to the cost of the house, but we're trying to save water in this case. 14,742 gallons of water saved is nothing to sneeze at. :)

posted by Caitlin @ CÂ³ on June 27th 2008 at 9:11am
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