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On the back of an envelope: Brush your teeth, but turn the water off

· Archived ScienceBlog

The Pacific Institute has done extensive and groundbreaking research over the past 25 years on a wide range of water, climate, energy, and environmental issues. One focus has been on how to use water more efficiently to do the things we want to do – a focus on “efficiency” and “productivity” – not deprivation.

Society could certainly cut water use by removing urban lawns, or never washing our cars again, or eliminating irrigated alfalfa in the desert. But we’ve never recommended these things. Why? Not because the water savings from such changes are small: some of these things can produce vast savings. But people don’t like to be “told” what to do. Instead, society reacts to “incentives” in the form of carrots (bribes? subsidies?), sticks (threats? taxes?), new technology, and education and information. All of these things help individuals and groups change behavior.

But despite our focus on the big issues of water-use efficiency and productivity, behavior and personal choice can still be important. Indeed, behaviors and societal preferences do change over time. Think about how society’s perceptions and preferences have evolved on issues like smoking on airplanes, or seat belt use. Think about civil rights, and women’s rights, and gay marriage.

In the water world, if our choices and decisions and behaviors change in the direction of lower-water-using options, so much the better.

Here is a simple, but significant figure. Kids often ask me if they should turn off the tap while they brush their teeth, rather than letting it run. I always gave this question little thought, given the far more dramatic and obvious water challenges of global agriculture, climate change, and industrial pollution and waste.

Until I got out the back of an envelope and played some numbers games. So, get out your envelope and let’s make some assumptions.

  1. You brush your teeth once a day (even though you tell your dentist you brush twice a day).
  2. You run the tap for 90 seconds while you put toothpaste on your brush, brush, and then wash out your mouth.
  3. Your faucet flows at 2.5 gallons per minute (a typical flow rate and the current standard for new faucets).

Under these assumptions, you use around 1400 gallons of water per year (2.5 gallons per minute times 1.5 minutes per day times 365 days per year).

What if we turn off the tap while brushing, turning it on only to wet the brush and then to rinse? Say 15 seconds in all?

Under these assumptions, you would only use 230 gallons per year, a savings of 1170 gallons per year or 84%.

Now, what if all 314 million of us – today’s population of the United States – changed our behavior?

Whoa. All of a sudden, we’re talking about saving 370 billion gallons of water a year.

That’s about a tenth the annual flow of the Hudson River, or the Colorado River, or (to use the silly but ubiquitous standard measure) would fill 560,000 Olympic-sized swimming pools.

These savings are real: This is water you won’t have to pay for, the water utility won’t have to collect, treat, and pump to you, and the wastewater utility won’t have to collect, treat, and throw away. And there are energy savings as well: all of these things require energy to do.

broken image

OK, silly picture, I admit. But you get the point. Turn off the faucet.

Feel free to play with these assumptions on your own envelope. Brush longer. Brush more often. Use a lower-flow faucet.

The kids are right. The sum of even modest individual actions can turn out to be significant.

Wait till I calculate the water implications of our diet choices…

Peter Gleick