How to Test for Bacteria in Water Bottles

Reusing water bottles has become a trend in recent years because using a bottle again is better for both the environment and your wallet. If you reuse plastic water bottles rather than ones specifically designed for reuse, however, bacteria can grow inside the bottles. If you want to test your water bottles to find out if they are contaminated or simply to see how much bacteria grows in a water bottle over use, you can conduct an experiment to find out.

Things You'll Need

• Petri dishes
• Pipettes
• Agar
• Hot water
• Unopened water bottle
• Used water bottles to test
• Permanent marker
• Incubator

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Instructions

• 1

  Mix the agar and hot water until the powder is completely dissolved.

• 2

  Fill the petri dishes halfway with the agar and hot water. Use one dish for each water bottle you are testing, plus one for the control.

• 3

  Open the unopened water bottle. This will be your control.

• 4

  Draw 2 milliliters of water out of the bottle using the pipette.

• 5

  Put the 2 milliliters of clean water in one petri dish using the pipette. Place the lid on the dish and mark it as the control.

• 6

  Draw 2 milliliters from a water bottle you wish to test. Use a new pipette. Put the 2 milliliters in another petri dish. Place the lid on it and mark it with a number. Mark the water bottle with the same number. Continue doing this for each water bottle you wish to test, using a new pipette and petri dish each time.

• 7

  Place the petri dishes in an incubator. Set the incubator to 110 degrees Fahrenheit. Leave the dishes for two days.

• 8

  Remove the petri dishes after two days. The control petri dish should look exactly the same. The ones that have bacteria will have pink spots on the surface of the agar, hot water and bottled water mixture. Each spot is approximately 100,000 bacteria.