How to Find the Amount of Bacteria in a Washed Water Bottle

Difficult-to-sanitize items like water bottles can be breeding grounds for bacteria, which harbor in the difficult-to-reach areas around the lid and base. Washing your water bottle may not remove all bacteria. If you are concerned about the cleanliness of your water bottle, you can perform a simple bacterial culture to determine the amount of bacteria present.

Things You'll Need

• Petri dish
• Agar
• Petri dish cover
• Sterile cotton swab

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Instructions

• 1

  Prepare a Petri dish with agar following the manufacturer's instructions. Once the agar has been prepared, tightly cover the dish to avoid contamination.

• 2

  Swab the inside of the water bottle with a sterile cotton-tipped swab. Run the swab over the entire inside of the bottle, taking care to swab around the lid, under the lip and in any crevices. Take care not to contaminate the experiment by touching the end of the swab.

• 3

  Lift the lid on the Petri dish slightly, and gently rub the swab across the agar. Discard the swab.

• 4

  Place the Petri dish in a warm, low-light environment. Allow the dish to sit undisturbed for 72 hours to allow bacteria to develop.

• 5

  Examine the Petri dish for bacteria. Each separate bacterial colony will appear as a dark spot on the agar. Spots that appear "furry" are actually fungus or mold colonies, rather than bacteria.