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Sunlight and bacteria growth in aquatic environmentsFeatured science projectScience project video


This science fair project was done to ascertain the relationship between the exposure of water to sunlight, and the amount of bacteria in the water. The science fair project experiment was performed on tap water, drain water and water from a lake.


The rate of bacteria growth in water will decrease after exposure to sunlight.

Scientific Terms

Bacteria, ultraviolet light, disinfecting


Solar Water Disinfection (SODIS)

One of the easiest ways of disinfecting drinking water is to fill the water in a transparent bottle and then place it under sunlight. If the water in the bottle is exposed to the sun for a sufficient amount of time, almost all the bacteria in it will be killed. This is possible because the ultraviolet radiation, plus thehigh temperatures, would be enough to kill all micro-organisms found in the water.

This method of disinfecting drinking water is gaining popularity in underdeveloped nations where sophisticated water filtration systems and clean drinking water are not readily available. The technique is known as "Solar Water Disinfection" (SODIS). It is very simple and economical because no initial investment or maintenance is required. Basically, only an empty bottle and sunlight is needed.

One setback for this method is that it does not work when strong sunlight is unavailable. The water needs 6 to 12 hours of exposure to sunlight before it becomes safe to drink. This method is only suitable for killing micro-organisms in the water. It does not remove other chemicals or heavy metal pollutants in the water.

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Time required:
1 day to prepare, 7 days for science fair project
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The bacteria should be destroyed before being disposed of. Pour some bleach into the petri dishes to kill all bacteria before disposable.