Waterworks: A Purification Process

Part of the Young Naturalist Awards Curriculum Collection.

by Kendra, Grade 8, Texas - 2006 YNA Winner

Would it be possible to make contaminated water safe to drink using something as universal and inexpensive as the sun's ultraviolet rays and simple plastic bottles? This was the question I asked myself when I read an article in the Standard Times about the Haitians' problems with their drinking water after Hurricane Jeanne devastated the island.

Kendra taking a water sample from the Concho River

Jeanne hit the island of Haiti in 2004, leaving behind a disastrous situation. Drinking water was contaminated with waste and other hazardous materials and products. The roads were impassable because of the damage sustained by the forces of wind and water. When trucks arrived with clean water, the thirsty islanders attacked them. Some people made a desperate choice to ingest contaminated water in order to survive, a choice that lead some to disease and even death.

If there is water, there is life—no water, no life. It's as simple as that, so it is very important to have a supply of clean water. And yet many countries still struggle to have clean water. In the Haitians' case, many different circumstances made clean, safe drinking water scarce. So, was there a way for the people of Haiti to make their own safe drinking water, or at least make it safer?

Yes, by UV. Specifically, by the sun's ultraviolet rays. It's free and it's everywhere. I knew that water-treatment plants used UV lights as part of the water-purification process. It is used along with other purifying treatments like reverse osmosis and carbon filtering. But could UV light alone be used to kill deadly bacteria? With this question in mind, I started my research.

Testing water samples for coliform bacteria

I discovered that I needed to test water samples for coliform bacteria. If there were coliform bacteria present in the water, then there was a good possibility that there were fecal coliforms present. This would indicate that there could be human waste present. And if there was human waste in the water, there would possibly be disease-causing pathogens present, pathogens that could lead to death.

I found a company, Micrology Laboratory, which sells a bacteria-growing nutrient called Coliscan Easygel. The nutrient contains special enzymes that cause coliform bacteria to turn pink and  E. coli  to turn purple. It was a great find because  E. coli  is a type of coliform bacteria found specifically in the intestines of warm-blooded animals. These two bacteria became my indicators for possible pathogens in the water.

Kendra adding Coliscan Easygel to her control sample.

So on a November day last year, I started a collection of water from the Concho River in San Angelo, Texas. I filtered the water with paper towels to eliminate some of the floating matter so that UV light could penetrate the entire water sample. I needed to lower the turbidity of my samples. I took a 1ml sample of water and added Coliscan Easygel as a control for my bacteria counts. I filled six bottles with the contaminated filtered water and labeled them. I set my bottles in the sun on a day with a high temperature of 68 degrees and a UV index of only 3.

I took 1ml water samples at two-, five-, six-, eight-, 9.5-, and 10-hour intervals. I decided to make sure the samples had maximum UV light exposure during the day, so the two-hour sample was exposed from 11 a.m. to 1 p.m., the five-hour sample was exposed from 10 a.m. to 3 p.m., and so on. After 10 hours (all the sun I had that day), my results were very promising. All  E. coli  had been eliminated from my samples, but a substantial amount of coliform bacteria was left, so I wasn't sure whether or not the water was safe to ingest. I decided to do some further testing.

Control results showing E. coli and coliform.
Exposed sample shows substantial coliform remains.

I knew I had to try another process to eliminate all the bacteria. After research, I came up with two agents: a 5% vinegar solution and 12% food-grade hydrogen peroxide solution. I found that both are used as disinfectants and are safe to ingest in controlled amounts. Even Heloise has given tips in her newspaper column for using vinegar to clean and disinfect items such as cutting boards and countertops. I also found that the food industry uses food-grade hydrogen peroxide to spray the insides of dairy containers and juice boxes before adding the ingredients. Even some ranchers have added food-grade hydrogen peroxide to their cattle's drinking water to help reduce infection and diseases in their cows. So I set out to find the answer to my second question: Could I eliminate all  E. coli  and coliform bacteria when I combined vinegar or food-grade hydrogen peroxide with the sun's ultraviolet rays?

There were several things I decided to change in this round of testing. Last year the high temperature on that November day was 68 degrees Fahrenheit, so this year I wanted to boost up the temperature. I knew that heat kills bacteria, because boiling water is a proven way to eliminate all bacteria and make water safe to drink. In order to achieve a higher temperature, I monitored the weather and chose a hot day in September to do my testing. This also changed the UV index. Last year the UV index was 3 on a scale of 12, and this year the UV index was 7. I also changed the amount of water in the 500ml plastic bottles. I put 250ml of contaminated water in each bottle, whereas last year I filled the bottles. I thought that maybe the amount of water in the bottles could affect the amount of UV light penetration. And I added my two different purifying agents, vinegar and hydrogen peroxide.

Readying samples
Exposing samples to UV
Creating a heat control

One thing I had to determine was the amount of vinegar and hydrogen peroxide to use. I followed the directions for consumption on the bottle of the food-grade hydrogen peroxide, and I used taste to determine how much vinegar to use. I added vinegar to 250ml of water until I couldn't stand the taste of it anymore.

I again collected my water samples from the Concho River and used the same filtering process I had used previously. I created a control using 1ml of water and adding the Coliscan Easygel.

Next, I performed the test. I added 1.5ml of food-grade hydrogen peroxide to one 250ml bottle and 5ml of vinegar to the other, and set them both in the sun. I also created a control for heat. After my first test I realized that in addition to the UV light, heat might have been a factor in killing the bacteria. So I placed a bottle with 250ml of water under a box in the sun to see how much of an influence heat had on my samples. The temperature outside was 102 degrees F. The temperature inside the box reached 107 degrees F. After eight hours, I collected 1ml samples from all three bottles. Both vinegar and hydrogen peroxide were successful in eliminating all the coliform bacteria. The heat control left 18 colonies of coliform bacteria compared to the original filtered control, which had 78, proving that heat could have affected the outcome.

Kendra adds purifying agent to water sample.

I then performed another test to eliminate the variables of UV light and higher temperatures. I filled three bottles with 250ml of contaminated water and added 1.5ml of hydrogen peroxide to one bottle and 5ml of vinegar to another. The third bottle I used as a control. I set them in a dark closet (away from any UV light) at a room temperature of 75.7 degrees F. for eight hours. This way I would know what effect adding vinegar and food-grade hydrogen peroxide alone would have on the bacteria, without UV light and high temperatures. The food-grade hydrogen peroxide eliminated everything, once again, while the vinegar left two colonies of coliform behind.


A bar chart titled: Total Coliform Colonies Hydrogen Peroxide as a Purifying Agent.
A petri dish with the hydrogen peroxide results. It appears clear, with no apparent bacteria colonies.
Hydrogen peroxide results
Control results

I also realized that time could have been a variable, so I decided to do one more test. I chose to test only the hydrogen peroxide because the vinegar had failed to eliminate all the coliform bacteria in the previous test. In testing the hydrogen peroxide, I eliminated the variable of time. I put 250ml of contaminated water into the bottle, added 1.5ml of hydrogen peroxide, shook the bottle, and immediately took a 1ml sample. The hydrogen peroxide eliminated everything!

Could the Haitians have used UV light and plastic bottles to make their water safer to drink? Yes. They could have added vinegar or food-grade hydrogen peroxide (if they had it) to purify their water even more. Would using any of these methods ensure that the water was totally safe? Probably not. There are other contaminates in water besides bacteria that can cause disease, like viruses and protozoa. Would these purifying agents eliminate these contaminates? I don't know. I will have to check it out.



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Bolton, Jim. Frequently Asked Questions About UV. Retrieved from the World Wide Web on 29 December 2005.

Clyde Co-op Company.  Hydrogen Peroxide: The Amazing Things They Don't Want You to Know . Retrieved from the World Wide Web on 29 December 2005.

Green Consumer.  Vinegar . Retrieved from the World Wide Web on 17 August 2005.

Guerrero, Oscar. Interviewed by Kendra Guerrero. 14 August 2004.

H2O2.com.  Introduction to H2O2 . Retrieved from the World Wide Web on 29 December 2005.

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Kalli, Ted.  O2 Plus Oxygen Emulsion Products . Retrieved from the World Wide Web on 20 January 2006.

Kentucky Water Watch.  Why Fecal Coliform Testing Is Important . Retrieved from the World Wide Web on 24 August 2004.

Micrology Laboratories.  Detection of Waterborne Coliforms and E. coli with Coliscan Easygel . Retrieved from the World Wide Web on 4 September 2004.

Mims, Joe. Doctor of Pathology at Shannon Medical Center, San Angelo, Texas. Interviewed by Kendra Guerrero on 8 and 9 November 2004, and 27 and 28 September 2005.

National Weather Service.  Stratosphere UV Index . Retrieved from the World Wide Web during November 2004 and September 2005.

Stouffer, Judy.  Vinegar and Hydrogen Peroxide as Disinfectants . Retrieved from the World Wide Web on 17 August 2005.

U.S. Department of Health and Human Services, Center for Disease Control and Prevention, and the National Institutes of Health.  Biosafety in Microbiological and Biomedical Laboratories . Retrieved from the World Wide Web on 24 August 2004.

Williams, David G.  The Many Benefits of Hydrogen Peroxide . Retrieved from the World Wide Web on 29 December 2005.

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