The Science of Backwash

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Can you prove that backwash happens? Does spit go back into the container you drink from?


The "How To" From Science-U

You Will Need:

  • Powdered drink mix (unsweetened - this does not taste good)
  • Bottle of water


  1. Put a spoonful of the powdered drink mix into your mouth and let it sit on your tongue for a few seconds.
  2. Take a drink of water from the water bottle.
  3. Observe if any of the colored drink mix goes into the bottle.

For educators and parents - How to guide young learners in science:

  • Inquiry-based learning (IBL) is a teaching approach that is fundamental for the development of higher order thinking skills (summarizing, analyzing, evaluating, creating). It puts the student in the driver's seat and promotes learning through engaging student-based investigations, following the same process used by scientists.
  • IBL begins by posing a question, problem, or scenario rather than simply presenting facts or a standard method to solve a problem. The learner is actively engaged and investigates concepts to reach authentic meaning.
  • The IBL process can vary, however the basics are as follows:

1. The student creates a testable question of their own.

2. The student obtains supporting evidence to answer the question by making observations, doing research, collecting data through an experiment, changing variables from a previous experiment, etc.

3. The student explains the evidence collected.

4. The student creates a claim (explanation) and justifies it using evidence form the investigation.

5. The student creates predictions for future investigations.

  • Recording information during the IBL process is also important to promote science literacy. The following chart is a helpful tool to guide students through the process.

Guided inquiry map

Questions to ask:

  • What does it mean that the water is colored after you drink it?
  • What does it mean if the water isn't colored after you drink it?
  • What would happen if you used a straw? Drank water out of a cup? Drank the water out of different types of bottles?
  • Can you change the way you drink to increase or decrease the amount of backwash that goes back into the container?

The science behind it:

  • Backwash is the term used for fluid which makes its way from a person's mouth back into a drinking container. When you drink from a bottle or a cup the liquid goes into your mouth and when you stop drinking, some of that liquid can be pushed out of your mouth and back into the container. The saliva that would be in the backwash contains bacteria, which is mostly harmless or helpful. However, when you're sick, you could be putting sickness causing bacteria back into the container and if someone else drinks from it, they could get sick too.


  • Teaching Great Lakes Science (
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