Bibliography

http://www.ehow.com/how-does_5188035_uv-light-kill-bacteria_.html
http://www.weatheronline.co.uk/Singapore/singapore/UVindex.htm
http://en.wikipedia.org/wiki/Ultraviolet
http://extoxnet.orst.edu/faqs/safedrink/microorg.htm

extras

Independent variable: 

-the length of time the water will be exposed to sunlight

Dependent variable:

-the amount of bacteria the water contains 

Controlled variable: 

-the amount of water in each zip blog bag

-the day of the experiment

-the water source that the water was taken from

Limitations:(from discussion)

-do not have an exact reading

-the climate in different countries differ-the result would not be the same as other countries
-the amount of sunlight on the day of the experiment

conclusion & discussion

graph indicating the results we received

Conclusion:

For the both sets of the experiment, the samples which have been placed in the sun have a significant decrease in the amount of bacteria when compared to the control sample. From this analysis, we were not able to confirm that placing the water under the sun would render the water drinkable. However, from the graph above, we can extrapolate that after 8 hours(recommended exposure time to the sun),the amount of bacteria would be at a percentage close to nil, thereby rendering the sample water almost bacteria free and hence drinkable. With reference to set 2, water sample A that was placed under the sun for 4hr had 7% more area on the  petri dish covered  with bacteria than water sample B that was placed in the Sun for 5hr. This proves that the longer the time the water samples are placed under the sun, the less bacteria it would contain. Our hypothesis that the UV light from the sun might be able to render water safe for consumption by killing the bacteria in the water have yet to be proven true.

Discussion:

So far, only the second set of experiment has proved to us that our hypothesis may be true. The incorrect results presented in the first set of experiment was probably caused by human error. We may have unintentionally spread more water onto Sample C than on A and B, thus causing the  incorrect results.For further experiments, we would ensure that there is an equal number of strokes drawn across the petri dishes with the respective sample water. After reviewing the experiment's processes, we realized that we have failed to compare the experiment to real drinkable water. In future experiments, we would test drinkable water sample and compare it to the rest of the experiment's samples. In addition to this, we plan to have longer and more even time intervals.