Dual Flush Dilemma
Julius Ballanco, PE
When I started in the plumbing profession, no one had the faintest idea how efficiently water closets flushed urine. Quite frankly, no one cared. The main problem was getting rid of the solids. The bowl evacuated the contents and fresh water was added.
It wasn't until they started to lower the amount of water that the flushing efficiency was actually measured. I'm talking about the lowering to 3.5 gpf, not the 1.6 gpf. When they went back and started measuring 5-gpf water closets, it was amazing how well the fixtures got rid of urine.
Keep in mind that in the 1960s, our government was so sure that water closets flushed fantastically that they identified a toilet bowl as a place to get drinking water in the event of nuclear fallout.
Then again, those were the days they had us run to the basement, sit against the wall, and place our head between our legs. Yes, that is a bygone era.
Getting back to water closet flushing performance. The means for determining how efficient a water closet removes urine is a test using blue dye. The dye is added to the bowl and a sample is removed. Then the bowl is flushed, and another sample is removed.
The flushing efficiency is the measure of the dilution rate between the two samples. The dilution rate is measured with a spectrophotometer. In other words, they are measuring how many shades lighter the blue dye becomes.
The old, 5-gpf water closets had a dilution rate of 10,000 to 1. Pretty good for getting rid of urine. Basically, the water was safe enough to drink in the event of nuclear fallout.
When the test protocol was established for 3.5-gpf water closets, a ratio of 100 to 1 was established. There was no particular reason for selecting a ratio of 100 to 1. The best thing that could be said was that the water didn't have any yellow tinge at 100 to 1. The 3.5-gpf water closets had no problem meeting this ratio.
When the flush volume was lowered to 1.6 gpf, no one saw any reason for changing the water exchange rate. As it turned out, 1.6-gpf water closets could also remove the water with a dilution ratio of 100 to 1. Of course, the test results showed that 1.6 gpf water closets were closer to the 100 to 1 ratio than were 3.5 gpf.
Lower The Urine RateIn 1999, I had a wonderful trip to Scotland to attend a meeting of the leading world plumbing research scientists. An interesting aspect of this trip was meeting people from all over the world. Of course, the hot topic was worldwide water usage and water shortages.
One of the individuals presenting a paper was Steve Cummings from Australia. Steve works for a company by the name of Caroma. Steve and I became instant friends. Steve is a lot smarter than I ever will be, and he has the letters after his name to prove it - Ph.D.
Here we were, two representatives from former British colonies, on British soil, talking about water closets. Steve was surprised that the Aussies and the Yanks were not the same when it came to our views on flushing water closets.
You see, in Australia, most modern water closets have a double flush handle; yellow for urine, brown for the other stuff.
Unlike the United States, Australia has a major water shortage. Dual flush water closets are considered a means of saving additional water by flushing half the amount of water when you urinate. The resulting daily savings of water per person equates to approximately 3.2 gallons of water. Multiply that by the population and the water savings adds up.
So, over dinner one night, Steve and I talked about water exchange ratios for water closets. (It's a good thing my beautiful wife, Judie, is used to these types of dinner discussions.)
Steve asked where the U.S. ratio of 100 to 1 came from. I said it was a nice round number and we know that the water won't look yellow.
He asked “Why not 17 to 1?”
I responded by asking, “Wouldn't the water have a slight yellow tinge?”
The response, “Maybe, so what?”
To which I said, “That's not cool, and the dog wouldn't like drinking the water.”
Steve commented, “The dog drinks out of mud puddles outside. Not a good subject for judging the quality of water.” Good point.
This lead to a lengthy discussion on the perceived hazards of urine. I learned more about urine than I ever cared to: it is sterile; during World War II, medics were trained to use urine when they had no other means for cleaning a wound, etc.
Introduction Of The Dual Flush WCSince our discussion in Scotland, the standard committee for water closets has discussed the lowering of the dilution ratio. Rates that have been discussed include: 50 to 1, 30 to 1, and 17 to 1. The new, lower rates may find their way into a revised standard next year. But then again, the updated standard could be further delayed.
In the meantime, Caroma has introduced their dual flush water closet to the United States. When you push the yellow handle, it flushes half the amount of water. Push the brown handle and you have a 1.6-gpf.
The water closet conforms to the ANSI standard at the 1.6-gpf rate. However, when using the yellow flush, the dilution rate is not 100 to 1.
Customer acceptance appears to be very high. The way I look at it, the yellow flush handle is better than the expression, “When it's yellow, let it mellow; when it's brown, flush it down.” A half flush is better than no flush.
Furthermore, the fixture responds to the conservationists' cry for more water savings by better efficiency.
U.S. manufacturers are paying close attention. If the American public buys into the dual flush concept, expect to see a lot more two-handle-flush water closets. This is an easy modification to the flapper and flush valve design that manufacturers can provide.