Measuring Water Wasted While Brushing Teeth

measuring water wasted while brushing teeth

Last week, a commercial came on TV about conserving water. The person in the ad made the statement that leaving the faucet on while brushing your teeth wastes 5 gallons of water each time you brush your teeth. My daughter asked me if that was accurate. I told her to measure it!


  1. Find a container to collect water from the faucet.
  2. Find a timer.
  3. Find one person to brush their teeth and one to run the timer.
  4. Start brushing your teeth, leaving the water on after wetting the toothbrush and shut the water off after the teeth are brushed and the teeth and toothbrush are rinsed.
  5. Be sure to start the timer as soon as the water is turned off and stop the timer when the water is shut off.
  6. Measure the collected water by pouring it into a container that has measurement lines (if your collection container does not)
  7. If your collection container is too small to hold all the water follow the following procedure: Time the toothbrushing process. Collect water in a container for 10 seconds and measure the amount collected. Use that measurement to figure out how much water would have been collected in the time it took to brush the teeth.

Results and Ideas For Further Study

We discovered that if my daughter keeps the water running while brushing her teeth, she uses 2.5 gallons. This was half of what the commercial told us. However, dentists tell us to brush a whole 2 minutes and adding rinsing time might bring the expected brushing time up to 2 minutes 20 seconds. My daughter only took 1 minute 30 seconds for the entire brushing process. She used less water, but might not have clean teeth!

Another variable to consider is the faucet. Different faucets have different flow rates. If the flow rate of your faucet is slow, you won’t use as much water in the same amount of time as you would with a higher flow rate faucet.

The findings from this project led to the next question.

How much water do I use when I just  turn water on for rinsing my toothbrush and my teeth? 

I guess that will be the next science project around here!

Why Is Water Conservation Important?

The earth’s water cycle does an excellent job in cleaning and processing our water naturally. However, our society uses more water than this process can keep up with. That’s why we have waste water treatment plants. They give mother nature a little help.

Although these water treatment plants are helpful, they use energy to clean the water and sometimes chemicals are necessary to get the job done. Conserving water reduces the amount of water that needs to go to these treatment facilities, therefore reducing the amount of energy used and reduces the amount of chemicals put into our water supply.

Why don’t you try this simple experiment? It’s perfect for Earth Day!

Looking for more Earth Day activities or want to win a great, new Ecology text for your family? Visit the Earth Day Activities post from yesterday.


  1. 1

    Jamie says

    Do people really leave the tap running while they brush? This is a tip I always see suggested to save water, but I don’t know anyone who actually leaves it running.

    • 2

      Marci says

      I’ve heard about people wasting water by leaving the water running when brushing teeth for years and I didn’t understand it either—until I had kids. They are always leaving it on! When I have asked others about it, I have heard more people talk about spouses, kids and friends who leave the water running. Who knew?

      Whether it is a big problem or not, my reasons for this project was merely to answer my daughter’s question. I think we might do it with the shower next. She takes so long to shower!!!

      • 3

        Azian says

        Hi, thanks so much for sharing these home experiments. i’m only just starting to home educate my daughter and i really like this one, cause it’s simple, yet has a very profound lesson about conserving water as well. this is great, i’m sure it will be one of my first “official” experiments at home 😉 thanks for the interesting info on this page, i will continue to look through it, it’s very enjoyable. greetings from NZ

        • 4

          Marci says

          Have fun with the experiment. I’m happy you found The Homeschool Scientist. There are lots of simple, effective experiments here.

  2. 5


    I have an attitude about the whole turning the water off, and it’s for a stupid reason. Way back in junior high they had us watch this over the top water conservation video, and John Ritter pops in and whispers how he likes to leave anonymous notes for people saying he saw them wasting water and leaving it on while brushing their teeth.

    All I could think while watching it was : 1. Nancy Drew taught me only cowards leave anonymous notes, and 2. I don’t want to be guilted into anything. So I still struggle with the attitude of “Oh yeah, let’s see you tell me what to do.” All because of a stupid video.

    That has very little to do with your cool experiment, just a random detail that pops into my head every time I see this brought up.


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