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. 

second set of experiments

	Control	A	B	C

Hours placed under the sun	0	4	4 1/2	5
Percentage of area nutrient agar covered	34%	11%	6%	4%

In the second set of experiments, the control has the highest percentage of area covered on the agar, followed by samples A, B and C respectively. Sample A that was under the sun for the shortest period of time had the highest percentage of area covered by bacteria on the nutrient agar. Correspondingly  sample C that was placed under the sun for the longest period of time had the lowest percentage of area covered.

set 2's result

first set of experiments

	Control	A	B	C
Hours in sun	0	4h	4&1/2h	5h
Percentage of area covered	30%	8%	4%	15%

Both sample A and B produced the expected result-Sample A has more bacteria than sample B-since it was exposed to sunlight for a shorter period of time. Sample C, on the other hand has significantly more bacteria than A and B. That should not have been the case since more bacteria should have been killed since it was exposed for the longest period(5h). Even though there was this particular anomaly, all the 3 samples which had been placed under the sun, had a significant decrease in the amount of bacteria as compared to the control sample.

% of area bacteria cover for control-30%

% of area bacteria cover for sample A-8%

% of area bacteria cover for sample B-4%

% of area bacteria cover for sample C-15%

procedure:)

We planned to exposed the water to the sun at time intervals of 2, 4, 6and 8 hours but some unexpected problems arose and we only managed to get the samples for 4, 4 &1/2 and 5 hours instead, which we thought would be indicative enough.

MATERIALS

-       Water from the reservoir

-       Measuring cups

-       Marker

-       Filter

-      zip blog bags

-      8 Petri dish

-       Agar

-       8 spreaders

-       Timer

Nutrient Agar

PROCEDURE

1.    Collect 5000of water from the reservoir.

2.    Filter 4000 water.

3.    Pour 500ml of water into 4 zip block bags respectively.

4.    Label (1), (2),  (3) and (4)on each of the bags using the marker.

5.    Place (1), (2) and (3) bags in a sunny place and (4) in a place without sunlight at all

6.   4 hours later, remove bag (1)

7.   4 & 1/2 hours later, remove bag (2)

8.   5 hours later, remove bag (3)

9.    Take spreaders, swipe the water from 1, 2 , 3 and 4 filtered water and wipe it on the agar in a zig-zag motion.

10. place the petri dishes at a temperature of 37 degrees for a day before taking it out of the controlled environment

11. Approximate the percentage of area the bacteria took up.

12. Repeat step 3-11 with another set of experiment

science SIA proposal

BACKGROUND

Water is not only a huge part of the environment, but it also plays an essential role in sustaining life. However, not all water is drinkable. In fact, most water is undrinkable. For example, water from a reservoir is not safe to  drink before it is chemically treated, filtered and disinfected. Filtration alone is not enough to free the water of harmful bacteria, making it safe for consumption. Exposing clear stream or lake water to direct sunlight(containing UV light), rendering the water drinkable is a known jungle survival technique among trekkers. UV light rays are heard to be an effective way to kill the bacteria in water and, presumably, other contaminants(microscopic organisms) in water Hence, in our experiment, we are trying find out how long the filtered water would have to be exposed to the sun before it can be safe for human consumption.

RESEARCH QUESTION

Hypothesis: The UV light rays from the sun might be able to render the water from the reservoir(filtered) drinkable-by killing the bacteria and other contaminants in the water.

How does the amount of time that the water from the reservoir is exposed to the sun affect the amount of bacteria present in the water at the end of the experiment?