Milk can be used to test the purity of water. Image credit

Milk can be used to test the purity of water. Image credit

ZIMSEC O Level Combined Science Notes: Testing the purity of water

Materials: 4 test tubes, sterilised fresh milk, tap water, borehole water, spring water. plugs


  1. Collect water samples from a borehole, spring and tap
  2. Pour out 5 cm3 of milk into each test tube and label each test tube with letters A-D
  3. Add 5 drops of  tap water to test tube B, borehole water to C and Spring water to test tube D
  4. Cover the test tubes with plugs washed in disinfectant and wiped dry
  5. Leave the dishes in a warm place for a few days

Results and Observations

  • The milk in test tube A was still fresh after a few days
  • The milk in test tube B was slightly sour
  • The milk in C was less fresh when compared to B
  • The milk in D was the most sour


  • Tap water is the safest, followed by borehole water and dam/spring/river water is the least safe to drink

To access more topics go to the Combined Science Notes page.

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