Resource: Water Treatment Plant

Print Background Essay

Early American settlers took water quality for granted. In lightly settled towns and villages in the 17th and 18th centuries, people found clean drinking water in nearby streams and lakes, as well as in wells they dug to access groundwater. However, as population densities increased in urban centers, many water supplies became contaminated, and people fell ill as a result of drinking the impure water. Between 1831 and 1832, tens of thousands of people died in Europe and the United States from a cholera epidemic, the result of drinking water contaminated with human waste.

Today, in developing countries around the world, disease-causing water-borne microbes and chemical contaminants sicken millions of people each year. For this reason, public health organizations have made sanitation a priority in an effort to provide all people with access to clean, fresh drinking water.

In developed countries such as the United States, government agencies require that the approximately 160,000 water treatment facilities supplying drinking water nationwide meet strict safety and quality standards. The Environmental Protection Agency (EPA) in the U.S. regulates the levels of dozens of potential contaminants, from the bacterium that causes cholera and the virus that causes Hepatitis A to lead, mercury, and arsenic. In most cases, the only allowable level of these contaminants is zero. Some chemicals, such as Chlorite, a by-product of some purification processes, are tolerated at low levels.

Public drinking water generally comes to a treatment facility either from underground aquifers or from surface streams and reservoirs such as the one featured in this video segment. Depending on the quality of the incoming raw water, treatment facilities use a variety of processes to make the water safe enough to drink. At the facility in Cambridge, Massachusetts, workers first add alum to the water. This chemical coagulates suspended particles, algae, protozoa, viruses, bacteria, and manganese into larger particles that float to the top as a "sludge" that can be skimmed off the surface. Facility workers then bubble ozone through the water to kill remaining bacteria, viruses, and protozoa. Next, they use activated carbon filters to remove organic compounds and any particles still in the water. Chlorine is then added to kill any bacteria that may have entered the water during the filtration process. The final step involves adjusting the water's pH level to limit corrosion in the public water system and, in some communities, adding fluoride to help fight tooth decay in the population.

To learn about how natural filtration creates drinkable groundwater, check out Earth Water Filter.

To learn more about the importance of water to life, check out Life's Little Essential: Liquid Water and Ingredients for Life: Water.

To learn more about Earth's water cycle, check out Water Cycle Animation and The Hydrologic Cycle.

To learn more about water conservation, check out Conserving Water at Home and Water Conservation: Denver, CO.

Print Questions for Discussion

• Where does the water that enters your home come from?
• Why is it important to treat water before sending it to homes?
• What do you think the brown sludge is made of? What other things do you think are removed from water to make it safe for drinking?
• Do you think all reservoirs prohibit swimming, fishing or boating? Why or why not?
• Water is becoming more contaminated and scarce. What can (or do) you do to conserve water? List 5-10 different ways.