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Bacteriology Science Fair Project

Bacteria in Water Bottles

Bacteria in Water Bottles | Science Fair Projects | STEM Projects
Are you curious about what happens when you don't wash your water bottle between uses? This science project will explore the bacteria content in water bottles when they are not properly washed.


The hypothesis is that bacteria will increase in a water bottle when it is not washed between uses.

Method & Materials

You will mark five water bottles with individual test subjects' names, one water bottle as a control, and give each test subject their water bottle in the morning. On the second day, you will refill the test subject's water bottle with water from new water bottles and give them back to the test subjects. On the third day, you will take the five water bottles used by the individual test subjects and the water bottle marked “control” to the lab for testing.
You will need 16 Kirkland brand water bottles, 16.9 fl.oz. (0.5 L), a Sharpie marker pen, 6 Gallon size Ziploc bags, 1 Roll paper towels, 12 Vials BHI agar slants, 10 ml. each, 1 Metal container to melt BHI agar in, 1 Bunsen burner, 6 Nalgene filtration units.  (115 ml capacity), 1 Pair of hot pad gloves, 1 Trivet , 1 Vacuum to filter the water, 6 Petri dishes, 1 Sterile scalpel, 1 Pair of forceps, 6 Disposable inoculating loops, 1 Incubator to incubate the bacteria, and 1 Autoclave.


The results of this experiment showed that the bacterial content in water bottles does increase when you simply re-fill your water bottle without washing it prior to re-filling it. Test subjects 1, 2, and 3 all had a high amount of bacteria colonies present compared to the control. Test subjects number and 4 and 5 had results that were significantly lower than the three other test subjects but there still was bacterial growth compared to the control sample.

Why do this project?

This science project is interesting because it shows how quickly bacteria can grow in a water bottle when it is not washed between uses. It also shows how important it is to wash your water bottle between uses to prevent bacteria growth.

Also Consider

Variations to consider include testing different types of water bottles and testing different types of liquids in the water bottle.

Full project details

You can find additional information and details for this science fair project here. Have fun exploring!

Related video

Hey there! Here are some awesome videos about this science project that we think you'll really like. They're not only super fun, but they'll also help you learn more about the science behind the project. So sit back, relax, and get ready to have some fun!!
This news station did a similar experiment, but the results would have been more solid if they included controls. What control would you add?
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