From Contaminated to Clean: How Filtering Can Clean Water
AbstractLiving in the industrialized world, like the United States, we are fortunate because we don't have to worry about the quality of our drinking water. Your community has the means to clean and provide water to you. But in many parts of the world, people don't have this luxury. Whether it is due to war or poverty, the lack of clean water leads to many health and social problems. In this environmental engineering science project, you will learn about different methods to filter out impurities in contaminated water, producing clean water for people who don't have access to it, and you will also experiment with filtering different kinds of liquids.
Michelle Maranowski, PhD, Science Buddies
To investigate the effectiveness of a simple filter column for filtering different kinds of liquids.
When you're thirsty, nothing is better for you than a glass of water. All you have to do is turn on the tap and fill your glass, open a bottle of water, or go to your refrigerator's water dispenser. Whatever method you use to get water, the point is that you don't have to worry about it. You can get a clean glass of water whenever you need it. However, many people in the world don't have this luxury. Their town or village might not have a well nearby and a family member might need to walk for miles to get the daily requirement of water. Or if there is water nearby, it might be contaminated. Contaminated water can be a source of deadly diseases, such as cholera and dysentery. According to the World Health Organization, every year approximately 1.6 million people die from illnesses (usually severe diarrhea) due to drinking unsafe water. Most of these people are children under the age of five. About 4,500 people—again mostly children—die every day because they drank unsafe water. Another side effect of lack of access to clean water is gender inequality. Gender inequality is the belief that one gender, male or female, is better than the other. The chore of gathering water for the family usually rests upon the shoulders of female family members, especially girls. If girls are gathering water all day, then they don't have time to go to school. Thus, access to clean water can result in a population that is not only healthier, but that is better educated, and more able to help improve their community because they are not sick. In the year 2000, the United Nations member countries put together the Millennium Development Goals. The purpose of this program is to reduce poverty and hunger, to tackle ill health, gender inequality, lack of education, lack of access to clean water, and environmental ruin. Access to clean water plays a big part in reaching many of the Millennium Development Goals. Figure 1 shows a young Rwandan boy enjoying a glass of clean water. This is one child that will not suffer the effects of severe diarrhea.
Figure 1. Young Rwandan boy having a glass of water while filling his water tank. (Courtesy of NASA, 2009.)
Since the start of the Millennium Development Goals program, many non-profit and for-profit companies have developed filtration tools that reliably clean water. These tools range from filtering straws that people can carry with them, to simple silver-lined (silver helps clean the water) clay pots. But what is a filter and how does a simple filter work? A water filter is a device that removes impurities (such as dirt) from water using a physical barrier, a chemical process, or a biological process. In this environmental engineering science project, you will experiment with a water filter column kit and see how it works to find out how effective it is at filtering color and visible particles from different kinds of liquids. The water filter column that comes in the kit has four sections: gravel, fine sand, activated carbon, and paper filter. The gravel allows water to pass through, but traps large particles. The sand allows water to pass through and traps smaller particles. The active carbon removes unwanted chemicals in the water through a process called adsorption. The last stage is a paper filter, which is effective at trapping oils. Many cities use water filters that are similar to the filter column you'll use in this science project. The additional step they take, however, is adding chemicals to the water to kill any pathogens, which could make you sick. While doing this science project, think about all the important science and technology that exists to improve people's lives, like devices to clean their water!
Terms and Concepts
- United Nations
- Chemical process
- Biological process
- Mathematical average
- What are the United Nations' eight Millennium Development Goals and how does clean water address these goals?
- What happens to your body when you have constant diarrhea?
- Can you describe three different tools for cleaning contaminated water?
- How does the water purification plant in your city work? Hint: Call your local water company to get more information.
- World Health Organization. (2010). Water Sanitation and Health (WSH). Retrieved June 22, 2010.
- United Nations Web Services Section, Department of Public Information. (2010). Water For Life, 2005-2015. Retrieved September 19, 2010.
- Wikipedia Contributors. (2010, June 11). Water filter. Wikipedia: The Free Encyclopedia. Retrieved June 22, 2010.
- Wikipedia Contributors. (2010, June 14). Water purification. Wikipedia: The Free Encyclopedia. Retrieved June 23, 2010.
- GOOD. (2010, July 22). Clean, Clear Water. Issue 016. Retrieved June 23, 2010.
- United States Environmental Protection Agency. (2010, April 21). Water Treatment Process. Retrieved September 19, 2010.
For help creating graphs, try this website:
- National Center for Education Statistics. (n.d.). Create a Graph. Retrieved July 16, 2010.
Materials and Equipment
- Green Science Clean Water Science Kit; available from Home Science Tools
- Bowls (3)
- Plastic spoons (1 box)
- Liquid measuring cup
- Teaspoon, ¼ measure
- Small bowl of garden dirt
- Vegetable oil, ¼ cup
- Medicine dropper
- Plastic cups, clear (9; 2 for each of the 4 liquids and 1 for a comparison water sample)
- Permanent marker
- Plastic wrap (1 roll)
- Sports drink, red-colored (1 cup)
- Tea kettle, small pot, or liquid measuring cup
- Mug (1)
- Tea bag; a bagged black orange pekoe tea (1 tea bag)
- Kitchen timer
- Cola/soda pop (1 cup)
- Lab notebook
- Graph paper
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Constructing the Filter
- Open the clean water science kit and read the enclosed instruction booklet completely.
First, open a packet of gravel and put it in a bowl. Rinse the gravel in water carefully three times to remove any dust.
- Open a packet of sand and put it into another bowl. Rinse the sand in water carefully three times. Swish the sand in the water and then let it settle before you carefully drain off the water.
- Open a packet of active carbon and put it into a clean bowl. Rinse the active carbon in water carefully three times. Clean the active carbon the same way as you cleaned the sand.
- Put the filter column together, as described in the instruction book.
- Prepare two filter plugs with wax, as instructed in the instructions, and insert them into two filter sections. Insert the other two plain filter plugs into two filter sections.
- Put the wet sand in one of the two filter sections with the waxed plug. Use a plastic spoon to scoop the clean sand from the bowl into the filter section. The sand will be wet, but try to scoop only the sand and not any extra water.
- Put the active carbon in the other filter section with the waxed plug. Use another plastic spoon to scoop the clean carbon from the bowl into the filter section. Avoid scooping any water into the filter section with the carbon.
- Put the gravel into one of the plain plug filter sections.
- Fold a filter paper in half and then in half again. Open the filter paper so that you have a cone or a funnel shape. Insert the cone into the last filter section.
- Construct the filter column, as shown in the diagram in the instruction booklet. Make sure that the bottom of the top filter section doesn't touch the material in the section below it.
Testing the Filter
- Make a contaminated water sample. Add 1/3 cup of water to the measuring cup. Add ½ teaspoon (tsp.) of garden dirt to the water and stir it with a clean plastic spoon. Using the medicine dropper, add a little vegetable oil to the water, approximately 4–6 drops. Mix the oil and the dirt completely into the water. Pour the contaminated water into a clear plastic cup.
- Place the filter column carefully on top of another clear plastic cup. Slowly pour a small amount of the contaminated water into the filter. The water should move between the filter sections drop by drop. Slowly filter about half of the contaminated sample. Continue to mix the contaminated water with the spoon so that the dirt doesn't settle.
Now compare the filtered sample of water to plain water and to the sample of contaminated water. Fill another clear plastic cup with plain water. Compare the clarity of the filtered sample to the clarity of plain water. Rank the clarity of the filtered water on a scale of 1 to 5, where 5 is very clear (as clear as the plain water) and 1 is murky, where the sample is not clear at all and looks identical to the original contaminated sample. Record this data in your lab notebook in a data table like the one shown below. You should also record any other observations that you make about the filtered water. For example, if the filtered water has grit in it, then record that in the table.
- Caution: This filtering device is not intended as a filtering device to make clean drinking water, only as a representation of more-advanced filters. Do not drink the filtered water.
- Boil 1 cup of water in a teakettle or small pot on the stove, or in the microwave. Place the tea bag in the mug and pour the cup of boiling water into the mug over the tea bag. Set the timer for 15 minutes and let the tea bag sit undisturbed for 15 minutes. Remove and discard the tea bag and let the tea cool down as you proceed with the following steps.
- Now take the filter apart and pour the gravel, the sand, and the active carbon into three separate bowls. Wash the three materials according to the instructions in the instruction booklet. Carefully unfold the paper filter and rinse it in water. Rinse the filter sections out in water. Refill the filter sections, remembering to fill one of the filter sections that has a waxed plug with sand and the other filter section that has a waxed plug with active carbon. Put the filter back together.
- Place 1/3 cup of sports drink in a clear plastic cup. Carefully place the filter on top of a clean clear plastic cup. Slowly pour half of the sports drink into the filter. The sports drink should move between the filter sections drop by drop. Slowly filter about half of the sports drink.
- Now compare the filtered sample of sports drink to plain water. Compare the clarity of the filtered sports drink to the clarity of the plain water in the cup from step 3 and to the original sports drink. Rank the clarity of the filtered sports drink on a scale of 1 to 5, where 5 is very clear (as clear as the plain water) and 1 is still colored and not clear at all (like the original sports drink). Record this data in your lab notebook. You should also record any other observations that you make about the filtered sports drink.
- Repeat steps 5–7 using 1/3 cup of tea. Record all data in your lab notebook.
- Repeat steps 5–7 using 1/3 cup of cola. Record all data in your lab notebook. Is the filtered cola just as fizzy and bubbly as the original cola?
- Repeat steps 1–9 two more times with clean materials (you can wash and reuse the plastic cups and use the remaining liquids you've already prepared). It is important to do the experiment at least three times so that you are sure that your results are repeatable and reproducible.
Analyzing Your Data
- Review the data that you collected in the previous section's data table. Average the rank data for each of the four liquids. Equation 1 describes how to average data. You can also ask an adult for help. Record the data in your lab notebook in a data table like the one shown below.
|Liquid||Average Clarity Ranking|
- Plot your data. You can plot your data by hand using graph paper or you can do your plots online at a website such as Create A Graph Label the x-axis Liquid and the y-axis Average Clarity Ranking.
- Did the filter remove all of the color and visible particles from the liquids? How effective is this filter at removing any visible particles from the liquids, such as dirt or food coloring? Did using this filter result in absolutely clear liquids as compared to each original liquid?
Ask an Expert
- The purpose of waxing the filter plugs is to slow the rate at which liquid flows through the filters. But what if you just can't wait to filter the liquid? Experiment with the rate of flow through the filter by changing the amount that you use to wax the filter plugs. Does changing the flow rate affect the quality of the filtered liquid?
- Try filtering teas that are brewed for different lengths of time. Brew tea for 10 seconds, 20 seconds, 5 minutes. Is the appearance of the filtered liquid dependent upon the length of brew time?
- Do some research at the library or on the Internet and make and test your own water filtration system.
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