Running Tap While Brushing Teeth

Here in Brazil people normally brush their teeth after having lunch, no matter where they are. Many even floss their teeth after meals. It is a good habit, definitely. I heard from some americans that if american people had the same oral hygiene people have here in Brazil, they would probably have much less dental care problems. I was not aware, but I assumed they have a lot of dental problems in the US since then. Well, of course, this probably doesn't apply to everybody here in Brazil, but this is how all our children are (supposedly) tought how to take care of their teeth.

It is very common to have the company's restrooms full of people brushing their teeth at 12:30p or 13:00p. And that's when this "little thing" happens. Some colleagues just can't brush their teeth without having water running from the tap they are using. They just can't help themselves. It is like this: They open the tap to use the water to make the toothpaste and the toothbrush moist, to start their brushing procedure. It makes sense and I do it myself, because this way it produces much more bubbles and foam. But I shut the tap close right after moisturizing my toothbrush. They do not. They leave the water running. Really running, at full flow. Sometimes I look at their running tap and make ugly faces and sometimes they stop the water. Some people only do it halfway, so they still have water (less water I must admit) running unnecessarily.

That's a lot of water!

The water utility company that serves our offices have put some "save water" stickers attached to the walls in our restrooms, right in front of the lavatory sinks. I don't think those water wasters are any sensitive to the stickers that states: "Fresh water: Making good use is easy. Living without it is hard.". I like those words. Just to let you know, I am not one of those eco-freaks or recycloholics, this thing just pisses me off.

There are one or two really cool online water waste calculators, but they are normaly used only to calculate how much water you're wasting by having dripping taps at home... Then I realized I should calculate the annoying-brusher-water-waste myself. For God's sake, I am an engineer, I can do this!

Bill of materials:

1. Toothbrush
2. Toothpaste
3. Stopwatch
4. 250 mL glass
5. Electronic spreadsheet

The Lab Setup

I timed: (a) how long I take to brush my teeth; (b) how long my tap takes to completely fill a 250 mL glass; and (c) how much time I keep the tap open and running when I brush my teeth. Results are shown below:

Time to fill 250mL glass	4.8 [s]
Time to brush	218.8 [s]
Yield	45.6 [glasses]
Total water	11.4 [L]
I keep tap open	32.0 [s]
Water I use	1.7 [L]
Wasted water	9.7 [L]

Every now and then I meet someone new with the same behaviour and because of that I estimate that at least 1% of the brazilian population have the habit of having water running while brushing. Again, estimating that only 1/10 of the brazilian population brushes three times a day, we would get to an alarming total of more than 5.35 million liters of wasted water each day (almost 2 billion liters each year).

My estimates can be inaccurate, but considering I have done the math only taking into account the brazilian population, it does not sound like a little thing and maybe shouldn't be on this blog after all...