Students learn about water quality testing (coliform bacteria, turbidity) and what is involved in basic water treatment designs. Biological, physical and chemical treatment processes are addressed, as well as physical and biological water quality testing, including testing for bacteria such as E.coli.

By creating access to clean water, engineers improve human health and save lives around the world. Engineers play a vital role in keeping harmful microscopic organisms out of our water supplies and research is continuously conducted to develop new ideas to lower the energy consumption and resource needs to do this. Engineers design large- and small-scale water treatment facilities and the water distribution systems that get the clean water to our homes and industries. bacteria coliform bacteria disinfection drinking water E. coli filter filtration microbiology microorganisms pathogen potable public health treatment plant turbidity water quality water treatment After this lesson, students should be able to: Describe how engineers determine water quality before deciding on water treatment options. Compare and contrast small-scale and large-scale water treatment options. Explain how water treatment technologies can save lives. Six thousand children die every day from lack of safe water! What can engineers do to decrease this fatality rate and increase health around the world? Engineers design easy-to-use water quality testing procedures, and simple and effective water treatment technologies. What's in water that causes so many deaths? The worst threats that hide out in water are pathogens, or harmful bacteria. Pathogens include disease-causing bacteria, such as E. coli (Escherichia coli), a type of coliform bacteria. Their presence in a water source is an indicator of water quality; high numbers of coliform bacteria indicate that the water has been contaminated with animal or human waste, such as sewage. Since sewage may contain pathogens, water containing sewage is considered unsafe. Some coliform bacteria are especially harmful, such as E. coli; others are a natural part of our bodies and are necessary to help us digest food and stay well. When good or bad coliforms are detected, it indicates to us that the water may be unsafe to drink. Turbidity is another test for water quality. Turbidity is a measure of the cloudiness of the water. Bacteria can feed off and hide in organic matter, which is what causes the cloudy and/or dirty appearance of water. Turbidity values also help us determine how to treat the water and what type of filtering system would be the most effective. Once we have determined the number of coliform bacteria present in a water sample and the turbidity of that water, we can begin to look at water treatment options. Treatment of a water supply varies, depending on the size of the system (water flow), the resources available, the incoming water quality, and the effluent (outgoing) water quality requirements. Effluent water quality standards are based on the World Health Organization (WHO) for international systems, and the Environmental Protection Agency (EPA) for U.S. systems. No absolute health-based guideline values exist for coliform bacteria or turbidity, but the WHO and the EPA provide recommendations (see Table 1). Coliform bacteria are measured by growing bacteria colonies and counting colony-forming units (cfu); turbidity is measured in nephelometric turbidity units or NTU. Engineers have improved the quality of life in industrialized countries (such as the U.S.) with the use of chlorine and the design of large-scale drinking water treatment and distribution (piped) systems that make safe water readily available to its populations. We sometimes take it for granted that we have water available inside our homes and feel confident that we won't get sick when we drink it. Engineers continue to research and test ways to improve these larger systems to increase safety and decrease their costs. Large municipal water treatment plants use chlorination and sometimes more advanced treatment technologies, such as ozone, membranes or ultraviolet (UV). A basic chlorination drinking water treatment system (see Figure 1) consists of six main steps: Roughing filter or settling basin to remove large particles and debris Coagulation and flocculation to induce opposite charges, which brings molecular-sized bacteria and harmful particles together to form even larger particles, followed by sedimentation to settle the now large groups of particles (flocs) out of the water Secondary filtration to remove bacteria, algae, and other small flocs still present Chlorination to destroy any remaining bacteria, viruses and pathogens Aeration to remove undesired odors or tastes caused by the previous steps Additional treatment, if necessary, such as adding lime (for softening) or fluoride When designing a system to provide drinking water to a large community, engineers consider more than just treating the water. They must find ways to deliver the clean water to every home and keep it clean in the process. A lot of engineering was needed to design the almost one million miles of pipe that span our country to bring us clean water! You can see that engineers are integral to cleaning and delivering safe drinking water to our homes and buildings. You can expect at least one — and maybe many more — large municipal water treatment plants in every big city. But, for small-scale, rural or developing communities, simpler water treatment systems make more sense. Engineers are continuously designing and implementing new ideas for these systems that improve the health and safety of people around the world, one community at a time. For these small systems, design ideas include: rainwater catchment systems — a method that collects rainwater from building roofs by connecting the top of the gutter downspouts to pipes that direct water to storage tanks slow sand filters — a system that uses long detention times of water above and within a sand bed to allow for biological activity to grow and remove pathogens point-of-use filters, such as the Filtrón — a filtering treatment at the point-of-use (or right as you pour a glass of water for drinking) Today, let's learn a little more about some of the engineering design that goes into the creation of all these large- and small-scale water treatment systems. According to the US EPA, drinking water may reasonably be expected to contain at least small amounts of some contaminants. The presence of contaminants does not necessarily indicate that water poses a health risk. EPA sets standards for ~ 90 contaminants in drinking water. Coliform bacteria are common in the environment and generally not harmful. However, their presence in drinking water is usually a result of a problem with the treatment system or the water distribution pipes, and indicates that the water may be contaminated with germs that can cause disease. Further, fecal coliform and E. coli are bacteria whose presence indicates that the water may be contaminated with human or animal wastes. Microbes in these wastes can cause short-term effects, such as diarrhea, cramps, nausea, headaches or other symptoms. Turbidity has no health effects. However, turbidity can interfere with disinfection and provide a medium for microbial growth. Turbidity may indicate the presence of disease-causing microorganisms. These organisms include bacteria, viruses and parasites that can cause symptoms such as nausea, cramps, diarrhea and associated headaches. Engineers design many types of simpler water treatment systems to use in small-scale, rural or developing communities. Following are more details on some of these systems. Rainwater catchment (RWC) systems are often an excellent option for communities or households in wet climates with a long rainy season. RWC systems are designed to store rainwater collected from the roofs of buildings by connecting the top of the gutter downspouts to pipes that direct water to large storage tanks. One concern with RWC systems is contamination of the water from dirt, leaves, bacteria and debris that accumulate on the roof between rainstorms. To help alleviate this concern, first-flush diverters are included as part of the system. These smaller tanks are sized to hold the first 1-2 mm of rain. With the first rainwater, the roof debris is washed off and sent to the first-flush tank. After the first-flush tank fills up, the rest of the (cleaner) water goes to the storage tank. Water is only used from the storage tank. A slow drain on the bottom of the first-flush tank releases its water, so that when more debris accumulates on the roof, it, too, is washed into the drained/emptied first-flush tank and not the storage tank. For more information, see http://www.rainwaterharvesting.org/index_files/FAQ.htm Since a slow sand filter provides a place for biological activity, it is also referred to as a biosand filter. As microorganisms, such as bacteria, viruses and parasites, travel through the sand, they collide with and adsorb (stick) onto sand particles. Most organisms and particles collect in the top sand layers, gradually forming a biological zone — a dense population of microorganisms that consumes pathogens (disease-causing organisms) as they are trapped in and on the sand surface. The first pathogens and bacteria are captured by the sand particles and then they eat the incoming pathogens and bacteria to stay alive, keeping the effluent (outlet) water free of pathogens. Slow sand filters are usually cleaned by scraping the bio-film and/or the top sand layer, leaving some of the biological layer behind to continue consuming the influent water pathogens. Slow sand filters are impractical for large cities, because flow rates are low and a large system would require a lot of land area. Slow sand filters can be a great choice for small communities since materials are inexpensive and usually readily available. For more information, see http://www.biosandfilter.org/biosandfilter/index.php/item/229 A point-of-use system is just as it sounds: treatment at the point-of-use, or right as you pour a glass of water for drinking. One example is a Filtrón, which is a simple, pressed terracotta (fired clay) bucket 11 inches wide by 10 inches deep (28 x 25 cm) made from local materials. Water is cleaned by filtering it through fine pores that are made by mixing a combustible ingredient (such as sawdust or rice husks) into the clay material that burn away when the pot is fired, leaving small pores. After firing, the pot is coated in colloidal silver, which has antimicrobial properties and kills bacteria that may slip through the pores. To use, the Filtrón is placed in a five-gallon plastic bucket with a lid and a tap. For more information, see http://ceae.colorado.edu/mc-edc/pdf/Filtron.pdf A one-celled microscopic organism (1-5 microns in diameter) that can, in some cases, cause disease. Chlorine atoms are used up as they kill viruses and bacteria in water. The chlorine residual is the amount of chlorine left at a particular point in the system. If no chlorine residual remains by the time the water reaches our homes, it is possible for the water to not be potable. A chemical that brings molecular particles together by introducing opposite charges. Any of several bacilli, especially E. coli, found in the large intestine of humans and other animals, the presence of which in water is an indicator of the presence of pathogenic bacteria and viruses. A measure of living bacteria cells. An abbreviation for Escherichia coli, a type of coliform bacteria that can cause serious illness in humans. Water (fluid) coming out of a system after being treated. Water (fluid) going into a system (often dirty or unsafe to drink). A disease-causing organism. (as applies to water treatment) A point-of-use system disinfects water right at the location where you collect and use it. Fit or suitable for drinking. Potable water is safe to drink. A measure of the cloudiness or haziness of water (or other fluid) caused by individual particles (suspended solids) that are generally invisible to the naked eye. Measurements of turbidity are used to indicate water quality and filtration effectiveness. A microscopic particle (20-300 nm in diameter) that can infect the cells of a living organism. Save a Life, Clean Some Water A lot of time, energy and money go into treating the water we use to drink, cook, clean and wash. We are fortunate to have safe water delivered directly to our homes as a result of the efforts of engineers in water treatment and water distribution systems. How does this affect our environment and the world? Engineers have helped to reduce the amount of sickness and death that result from contaminated drinking water. The contamination often comes from pathogens or harmful bacteria, such as E.coli. What are two indicators of water quality? That's right, water quality can be measured through the presence of coliform bacteria in a water sample and the turbidity of that water. Large-scale water treatment systems used in larger cities include steps for filtering, coagulation and flocculation, sedimentation, chlorination and aeration, as well as (sometimes) lime (for softening) and fluoride. After all this, we often don't even realize that our water has been treated before it gets to us. Engineers also help people in remote and/or developing countries improve their water quality and health. What are some of the small-scale water systems engineers design and install? That's right: rainwater catchment systems, slow sand filters, and point-of-use filters, as well as small-scale distribution and piping systems from nearby water sources. The development of water treatment technologies by engineers saves lives around the world. Discussion Question: Communicable diseases represent seven of the top 10 causes of child mortality in developing countries around the world! And, they account for about 60% of all child deaths! (Write the causes listed in Table 2, in random order, on the classroom board.) Can you work together as a class to put them in order from what you believe to be the most deadly to the least deadly? When you finish, I will tell you the actual statistics for the percentages of deaths. (Most diarrheal illnesses are attributable to inadequate drinking water, sanitation and hygiene.) Then, you'll create a pie chart to show their relative impact. (Conclude by asking the students the following question.) How could we, as engineers, help decrease the second leading cause, diarrheal diseases, and save children's lives around the world? Data source: http://www.who.int/whr/2003/chapter1/en/index2.html Idea Web: Ask students to brainstorm a list of ways that water can be polluted. (Possible answers: From factory chemicals, animal and human waste, pesticides.) What effects do these pollutants have on us and our environment? (Possible answers: In the short term, they might make us sick. In the long-term, they can upset the natural balance and keep people, animals, soils and plants from ever being well, leading to death.) What are possible solutions for reducing these types of pollutants? Bingo: Provide each student with a sheet of paper to draw a large tic-tac-toe board (a 3 x 3 grid with nine squares) that fills the entire paper. Have students write a vocabulary term in each square, in any order they choose. To mark off squares, have students walk around the room and find other students who can each accurately define one vocabulary term. Students must find a different student for each term. When a student has all terms completed s/he shouts "Bingo!" Continue until two or three students have bingo. Ask the students who shouted "Bingo!" to give definitions of the vocabulary terms. Find the Solution: What other simple and low-cost water treatment solutions can you find? Look online for other methods or systems that bring clean, safe drinking water to communities around the world. Keep in mind that materials and money are limited in small villages. Start your investigations with the World Health Organization (WHO), Water for People, or Engineers Without Borders-USA. Cite your sources, including at least two other than the three provided. Engineering in Politics / Class Discussion: Solicit, integrate and summarize student responses. What are your thoughts on the following statement from a national report on drinking water distribution systems in the U.S.? Of the 34 billion gallons of water produced daily by public water systems in the U.S, approximately 63% is used by residential customers. More than 80% of the water supplied to residences is used for activities other than human consumption, such as sanitary service and landscape irrigation. Nonetheless, distribution systems are designed and operated to provide water of a quality acceptable for human consumption. Source: "Drinking Water Distribution Systems: Assessing and Reducing Risks," Summary, Water Science and Technology Board, 2006, http://www.nap.edu/catalog.php?record_id=11728 Are you willing to pay for municipal water treatment so that all the water we use to flush our toilets and irrigate our yards is safe enough for drinking? As an engineer, would you design things differently? If you were an advisor to the President, what recommendations or changes would you make about our country's current water system? Are we making the best use of our money and resources? See a side-view cutaway diagram of a Filtrón point-of-use water treatment system on the cover of the Belize Filtrón Feasibility Report by Engineers Without Borders at: http://ceae.colorado.edu/mc-edc/pdf/Fahlinreport02.pdf See a slide show titled, "Evaluating the Water Treatment Effectiveness of the Filtrón," at http://ceae.colorado.edu/mc-edc/pdf/BielefeldtMascaro05Filtron.pdf What is turbidity and why is it important? How to use a Secchi disk to measure transparency? See the EPA's Monitoring and Assessing Water Quality website at http://www.epa.gov/owow/monitoring/volunteer/stream/vms55.html Drinking Water Contaminants, Ground Water and Drinking Water. Last updated July 27, 2009. US Environmental Protection Agency. Accessed December 10, 2009. http://www.epa.gov/safewater/hfacts.html Filtrón Offers Promise of Clean Water to Families Throughout the Developing World. Last updated July 23, 2009. Mortenson Center in Engineering for Developing Communities, College of Engineering and Applied Science, University of Colorado at Boulder. Accessed December 10, 2009. http://ceae.colorado.edu/mc-edc/pdf/Filtron.pdf Guidelines for Drinking-Water Quality (third edition, incorporating first and second addenda). 2008. Volume 1 - Recommendations. World Health Organization, Geneva. Accessed January 13, 2010. http://www.who.int/water_sanitation_health/dwq/gdwq3rev/en/ Harvesting Rain… But Is It Really as Simple as That? FAQs. Rainwaterharvesting.org. Centre for Science and Environment. Accessed December 10, 2009. http://www.rainwaterharvesting.org/index_files/FAQ.htm Huisman, L. and Wood, W.E. Slow Sand Filtration. 1974. World Health Organisation, Geneva. In The Biosand Filter. BioSandFilter.org. Accessed December 10, 2009. http://www.biosandfilter.org/biosandfilter/index.php/item/229 National Primary Drinking Water Regulations. May 2009. US Environmental Protection Agency. Document #EPA 816-F-09-004. Accessed January 13, 2010. http://www.epa.gov/ogwdw000/consumer/pdf/mcl.pdf Surviving the First Five Years of Life: Causes of Death in Children. The World Health Report 2003, Chapter 1: Global Health: Today's Challenges. World Health Organization. Accessed December 10, 2009. http://www.who.int/whr/2003/chapter1/en/index2.html Turbidity. Last updated December 3, 2009. Wikipedia, The Free Encyclopedia. Accessed December 10, 2009. http://en.wikipedia.org/wiki/Turbidity