
Sunlight and Bacteria in Water
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Does sunlight reduce the number of bacteria in water? Ultraviolet rays from the sun can damage bacteria cells. This project tests whether that effect works on real water sources.
You collect water from three different sources. You swab samples onto agar dishes before and after leaving each water bottle in sunlight for two days. After five days of growth, you measure the bacteria colonies.
The results show how much smaller the colonies are in sun-exposed water.
Hypothesis
The hypothesis is that the rate of bacteria growth in water will decrease after exposure to sunlight.
Method & Materials
You will prepare 6 agar petri dishes, and use swabs to collect water from different sources. You will then place 3 bottles of water in direct sunlight for 2 days, and measure the amount of bacteria growth in the petri dishes after 5 days.
You will need 6 agar petri dishes, 6 disinfected swabs, 1 bottle of disinfected water, 1 transparent bottle filled with tap water, 1 transparent bottle filled with water collected from a drain, 1 transparent bottle filled with water from a lake, 1 ruler, and 1 marker pen.
Results
The results showed that the amount of bacteria growth in the petri dishes was much lower for the water that had been exposed to sunlight for 5 days. This proves that the hypothesis was correct - the rate of bacteria growth in water does decrease after exposure to sunlight.
Why do this project?
This science project is interesting because it shows how a simple and economical method can be used to disinfect drinking water in underdeveloped nations.
Also Consider
Experiment variations to consider include trying different lengths of time for the water to be exposed to sunlight, and comparing different colored bottles or glass and plastic bottles.
Full project details
Additional information and source material for this project are available below.Related videos
These videos explain the science behind this project and demonstrate key concepts used in the experiment.
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