Calculating the Savings of a Dual-Flush Toilet

Calculating the Savings of a Dual-Flush Toilet

Jonathan B.
Jun 25, 2008

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

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