Clean Water. Part 2.
July 01, 2016
Last month, we began our investigation of Clean Water, particularly the history of water treatment. We learned that, as a direct result of water treatment, “By the beginning of World War II, typhoid, cholera, and dysentery were, for all practical purposes, nonexistent in the United States and the rest of the developed world.” It’s not therefore surprising that the CDC calls the last century of water chlorination and treatment “one of the Ten Greatest Public Health Achievements of the 20th Century.”
As the incredible results of water treatment became more apparent, the U.S. Public Health Service set standards for water purity, standards that have been revised over the years, as new contaminants have been identified. Modern water systems carefully monitor water throughout the treatment process for traces of chemical pollutants and microbes; they have sophisticated computerized devices capable of detecting contaminants in the parts per trillion.
Drinking water utilities use various methods of water treatment to provide safe, clean, healthy drinking water for their communities. Water may be treated differently in different communities depending on the quality of the water that enters the treatment plant. Today, the most common steps in water treatment include:
Coagulation and Flocculation
Water treatment usually begins with Coagulation and flocculation. This entails adding positively charged chemicals to the water. The positive charge of these chemicals neutralizes the negative charge of dirt and other dissolved particles in the water. When this occurs, the particles bind with the chemicals and form larger particles, called floc.
During sedimentation, the heavier weight of those larger particles (floc) causes the floc to sink, settling at the bottom of the water supply. This settling process is called sedimentation.
"Once the floc has settled to the bottom of the water supply, the clear water on top will pass through filters of varying compositions (sand, gravel, and charcoal) and pore sizes, in order to remove dissolved particles, such as dust, parasites, bacteria, viruses, and chemicals.”
After the water has been filtered, a disinfectant such as chlorine may be added in order to kill any remaining bacteria, viruses, or parasites, and to further protect the water from germs.
“To learn more about the different treatments for drinking water, see the National Drinking Water Clearinghouse's Fact Sheet Series on Drinking Water Treatments.
To learn more about the steps that are taken to make our water safe to drink, visit the United States Environmental Protection Agency's (EPA) Public Drinking Water Systems webpage. To learn more about the 90+ contaminants EPA regulates and why, visit EPA's Drinking Water Contaminants page.”
Figure courtesy of the EPA
Consumer Confidence Reports
Every community water supplier must provide an annual Water Quality Report, sometimes called a Consumer Confidence Report, or "CCR," to its customers. The report provides information on your local drinking water quality, including the water's source, contaminants found in the water, and how consumers can get involved in protecting drinking water. For more info, view the CDC's guide to Understanding Consumer Confidence Reports
Great Achievements, http://www.greatachievements.org/?id=3614