Significant Figures by Peter Gleick

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.

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

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

Comments

  1. #1 musubk
    United States
    February 21, 2013

    I’ve been living in a cabin with no running water for the last 2.5 years, meaning all my home water use is carried home by hand in jugs. Makes you pretty conscious about how much water you need to use. When I brush my teeth, I put a little water in a cup, and that’s all I use. Dip the brush in to wet it, brush your teeth, swish the brush around in the cup to clean it, then rinse your mouth with what’s in the cup, or just spit without rinsing. I use literally half a teacup of water to brush my teeth. Something to think about for anyone who just decided now is the time to change a habit.

  2. [...] the planet, I also read an interesting article today about how much water can be saved by simply turning the faucet off while you’re brushing you [...]

  3. #3 Sagheer Aslam
    Montreal, Canada
    February 21, 2013

    Yes. These savings are real. Second assumption can be taken as 120 seconds. Reason for that is increase in the timer-based tooth brushes (based on 2 minutes), and various advertisement and schools recommending 2 minutes brushing time. It can be assumed that those who take less time (less than two minutes) are balanced by those who brush twice a day. In all cases its SIGNIFICANT.
    A 48 seconds video tu support the message:
    https://www.facebook.com/home.php?ref=hp#!/photo.php?v=4763403243338

  4. #4 G
    February 22, 2013

    What I do:

    The “purge water” in the shower (the cold water that comes in before it gets hot) goes through a valve on the showerhead and into a storage tank. There are two such tanks in the hallway.

    When both are full, one of them is used as input to laundry to wash a load of clothes. (Having two tanks and only using one at a time also ensures I have a full tank of water at all times in the event of an earthquake: no need to buy bottled water for this.)

    The graywater output from the laundry is used to flush the toilet. (You can do this yourself by simply storing it in your laundry tub and using a bucket to flush the toilet.)

    Net savings better than 20% of total indoor water use. And the whole cycle can be automated easily enough, to the point where people don’t even notice it’s being done. (Feel free to pull my email address from this post if you want to get in touch about this.)

    As for tooth brushing, this is much easier when sinks are equipped with foot-pedal controls, so you don’t have to keep a hand on the faucet.

    But as for lawns: those enormous water-wasters will go away as the culture changes. Which can be done quickly enough via the media. Envision a public service ad showing Dad snoozing in the hammock, the kids playing basketball in the driveway, and a nicely landscaped non-lawn yard, with the voice-over saying “You have a lot more free time when you don’t have to deal with a lawn. Save water, have fun.”

  5. #5 ecologist
    February 22, 2013

    Speaking of incentives … my town bills for water on a amount-used basis ABOVE a minimum amount. Use any amount less than the minimum amount and you still pay the same water bill. I don’t think I have ever used more than the minimum (I have either had a small family or been living alone). So, I have no financial incentive to become more efficient at water use. (I try to anyway).

    I suspect that this is a common way for towns to charge for water (true?). Do you have any thoughts on trying to get this changed, so that there would be incentives for economizing for more people (or for everyone)? What kind of resistance does this usually encounter?

  6. #6 Peter Bellin
    United States
    February 22, 2013

    I turn the water off; it makes little sense to keep it running. We also collect the cold shower water in buckets and use that water for other purposes.

    I think that there should be guidelines for per person water use; I can calculate for our household. We try to keep below 40 gallons per person per day. With a target in mind, a family can take the actions needed to reduce water (or other utility) use.

  7. [...] Personal choices do matter, says Peter Gleick:  ” … 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. … “  So how much difference can a personal choice make, such as turning off the faucet when you brush your teeth?  Peter Gleick does some calculations: On the back of an envelope: Brush your teeth, but turn the water off [...]

  8. #8 G
    February 26, 2013

    Yo Ecologist- Here’s how that works:

    Your city water utility’s baseline charge reflects the cost of maintaining the common infrastructure: reservoirs or wells, water storage towers if any, water purification system, and water mains under the streets.

    It’s like your phone bill: the basic charges cover the cost of the central office & outside plant, and then you pay additional for long distance calls.

    What to do about this:

    Clearly it would be better if the city changed its bills to read something like this:

    “Water supply common infrastructure cost: $XYZ.
    Water cost per gallon: $Q.
    Number of gallons used in previous billing cycle: RRRR.
    Cost for water used: $ABC
    Total bill this cycle: $DEF.”

    Everyone pays the same basic charge for infrastructure, and then they pay for gallons used. The costs could remain the same at the bottom line, but spelling out the cost of water actually used, provides an incentive for conservation.

    Yes this will probably boost everyone’s water bill by some small amount, but adjustments could be made in the price per gallon for usage below some minimum amount.

    Talk with anyone who has small business management experience (spreadsheets, accounting, business planning), and they can help you figure out the best way to set it up and present the financial information to the water department. Then go to the water department with a serious proposal to change the wording on the bills. You’d be surprised how receptive public officials are when you come in with a specific and detailed proposal.

    Yo Peter-

    Right on! And anyone can save that purge water from the shower, to use for (whatever). The garden, toilet flushes, input to laundry, are all viable uses for it. The simplest thing is to just collect it in a 5-gallon pail and use it for toilet flushes, because you don’t even have to carry it outside the bathroom. However, keep an additional 2-gallon pail in the bathroom as well, because it’s much easier to pour the water from a full 5-gallon pail into a 2-gallon pail, and measure and flush from a 2-gallon pail, as compared to trying to flush directly from a 5-gallon pail.

    The Big Dirty Secret of course, is that agricultural use is the major source of water wastage in most areas, and the most resistant to change. However, getting people to conserve does make a difference in terms of demand for _potable_ water, and it also produces “buy-in”, in the sense that people who do it are more likely to start doing other things as well, both water-related and other, such as driving less, turning down their heat and air conditioning, etc.

    Everything counts, and everything is connected to everything else.

  9. #9 Juggling Physicist
    California
    February 27, 2013

    I have a question.

    I’m all for preserving ground/river water for the ecosystems that need it. I understand that when you use water for agriculture, washing the car, or watering the garden, that water evaporates and it’s not available anymore for the rivers and streams. But when you run extra water through the sink or shower, doesn’t that water eventually run back into the river or groundwater after being processed?

    I understand that it takes energy to upkeep the water infrastructure, pumping, etc… so that causes each bit of extra water used to have more impact on the environment. But the water itself — it’s not really “wasted”, is it? Doesn’t it go back into the environment?

    • #10 Peter Gleick
      February 27, 2013

      Excellent question. Some of our water use is “consumptive” in the sense it is used and made unavailable for use elsewhere in the same watershed. Most agricultural water use is consumptive. Some is “non-consumptive” if it is captured after use, treated, and made available for reuse. In California, it depends both on what the “use” is and on /where/ you are. Non-consumptive use inland can (and sometimes is) reused. But on the coasts, much of our treated wastewater is thrown away and not reused. Yet. And overall, the amount of water on the planet stays the same, but that doesn’t help us on a regional level is we don’t capture and reuse our wastewater, or if much of our water use is consumptive and disappears from our basin.

  10. #11 DanielC
    NZ
    March 2, 2013

    To elaborate on Peter’s response, it’s not just quantity that matters but also, quality, timing, and location. Municipal waste water may be enriched with nutrients or pharmaceuticals which the receiving ecosystems may not appreciate. The returned water usually doesn’t go back to where it was taken from. And impounding water in reservoirs can change the variability of flows which are themselves quite important for ecological functions.