Low-Flush Toilets

Low-Flush Toilets Photo Credit: Clipart.com

Over a decade ago, the Department of Energy began mandating the sale of low-flush toilets. They're designed to use less than half the water per flush as a standard toilet, but scientists have wondered whether they really save as much water as they're supposed to—especially after a few years on the job. In this Science Update, you'll hear about a recent study that looked at just how well low-flush toilets stand the test of time.


Getting a window into the bathroom. I'm Bob Hirshon and this is Science Update.

Gary Woodard, a water researcher at the University of Arizona, knows a lot about the toilets in Tucson. As a case in point, he pulls out a graph showing what happened inside one house on a Saturday morning.

This was a couple of toilet flushes. I can tell that these were two different toilets. I can tell that the one toilet's using about a gallon and a half, just as it should. But the other one is using significantly more.

These are just some of the details from a recent study by Woodard and his colleague Jim Henderson. They put sensors on the outdoor water meters of two hundred households in Tucson—recording and then analyzing every flush, drip, and drain. Among their many findings was the discovery that about 43 percent of the low-flush toilets in the study had problems due to aging.

Once a toilet's installed, it can remain there for decades. So if after just 7 or 8 years, nearly half of them are starting to waste water, then you've got a serious problem.

He says studies like these that get an accurate picture of water usage could lead to more effective conservation programs—by showing exactly where water's being wasted and how it can be saved. For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

Although the toilet-flushing habits of Arizona residents are certainly ripe fodder for any party conversation, this study is also interesting because of the procedural issues involved.

For one thing, there's the way the study was carried out. To measure water use in their study households, Woodard and Henderson used outdoor water meters that the residents didn't know had been installed. Why? Well, it turns out that it's actually very difficult to measure how much water people use. If you ask people to report it, they're not very reliable. If you put little meters on all the water-using appliances in the house, people tend to use less water because they know someone is watching how much they use. That's an illustration of a principle called the Hawthorne effect: the very act of measuring something changes the thing being measured.

With their sensors surreptitiously attached to an outdoor water meter, the researchers were free to measure the way families use water on a day-to-day basis. The downside was that there was only one meter. So the scientists had to try and deduce what appliances were being used when, simply by looking at the total amount of water used by the entire house.

To do this, Woodard and Henderson learned how to interpret the water patterns that they measured. For example, looking at a graph of water use throughout the day, two big peaks close together in time suggest a clothes washer. (That's because clothes washers use a lot of water and have two distinct cycles: wash and rinse.) A dishwasher has three or four smaller peaks. When someone takes a shower in a bathtub, there's a big spike right before the shower begins as they let the water flow through the lower faucet to warm up. With enough practice, the researchers learned to identify most major water-consuming appliances in the house.

As the report suggests, it turns out that many low-flush toilets weren't holding up well over time. Some began to waste water; others were so weak that people had to flush them twice. (In a few unlucky cases, the toilets exploded!) Woodard believes that some of the problems can be fixed by adopting industry-wide manufacturing standards for low-flush toilets, as studies like his reveal which parts last well and which ones eventually tank.

Now try and answer these questions:

  1. Why would scientists be interested in the amount of water different appliances use?
  2. What are some of the difficulties in measuring everyday household water use?
  3. What other kinds of behavior might be difficult to study if the people know they're being studied?
  4. In Woodard and Henderson's study, which kind of appliance would be easier to keep track of: a hot tub or a coffee maker? Why?
  5. How many different water-using appliances do you usually use in a day? How many gallons of water do you think that consumes? (Once you've guessed, click here to find out the averages.)
  6. The Supreme Court has ruled that it's illegal for the police to spy on people—for example, by using heat-sensing thermal imaging to see through houses—if they don't have other evidence that they may be committing a crime. In a research study like this, the investigators are effectively "spying" on their subjects. Do you think there's a difference? Why or why not?
  7. Click here to find out the guidelines for conducting this kind of research. After reading the guidelines, did your answer to #6 change?

For Educators

On the Sustainability of semi-Arid Hydrology and Riparian Areas (SAHRA) website, you can read Gaining Insights on Domestic Water Demand through Remote Sensing. On page 3 is a graph of water use for a household included in Woodard and Henderson's study.

On the Residential Water Conservation site, you can see how water can be wasted throughout a house and its surrounding lot. Click on the bathroom and then the toilet for more specific information about the low-flush technology.

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