Utility Watchdog in San Diego

Dual Flush Toilets - Money Saver or Snake Oil?

Dual flush toilets may be another defining moment in the development of the American john: the introduction of environmental conservation to the process of elimination. Interest in low flow and dual flush toilets is on the rise in the United States, due in part to increased government regulation and the rising cost of water, and there are incentives for making changes in the way we use the commode.  Change may be a good thing, learn more about the specifics of the dual flush and find out how government and business are coming together to help America flush responsibly saving both money and water.

It's fairly simple to figure out your cost savings. You take the number of gallons per flush with your old system multiplied by the amount of flushes per year to get your annual toilet water use. You then determine how much water your new flushing system uses per year and subtract. This is your water savings in gallons per year. Since the City of San Diego charges you by hundred cubic foot (HCF) of water, you need to convert gallons into HCF. There are 748.05 gallons per HCF.

Here's a simplified model to see how much water you save. Let's say you live in a home with another person (two people total) that share a toilet. The toilet uses 3.5 gallons per flush. At an average of 10 flushes a day (5 for each person), the single flush toilet uses 12775 gallons per year.

The dual flush system touts that it can save up to 70% water per flush. That's probably half-marketing, half-truth, so we'll say that the dual flush system will save 50% water per flush. This means that instead of using 3.5 gallons per flush, the toilet will use 1.75 gallons per flush. The annual water use is cut in half, to 6387.5 gallons per year saved. That's a lot of water! But, how much does it actually save you?

6387.5 gallons of water is approximately 8.53 HCF. To find out your annual cost savings, we simply need to multiply the HCF saved by the City's charge per HCF.

Currently, the San Diego City Water Department has three tiers. In the first tier, water is $3.612 per HCF; the second tier is $3.917 per HCF; and the third tier is $4.398 per HCF. This means a two-person household flushing the toilet 10 times a day will save $28 per year in the first tier, $30 in the second tier, and $34 in the third tier.

While those eagle eyed readers will point out that these numbers are nowhere near $100 a year, this doesn't mean that certain people won't see those types of savings. A family of 4 could easily hit the $100 per year savings, and larger families would save even more money.

Depending on your current toilet water use, you potentially could see a large drop in your annual water bill. However, if your toilet doesn't use that much water, your cost savings may be minimal. That being said, it is always great to conserve water.

About UCAN

UCAN has represented the interests of San Diego County utility customers since 1983. UCAN focuses its efforts on the rates and services of San Diego Gas and Electric Company, telecommunications utilities and the City of San Diego Water Department.