Americans are fortunate to live in a country with one of the safest water supplies in the world. According to the Environmental Protection Agency (EPA), 286 million people get their drinking water from a community water system. To make water safe for public consumption, it undergoes a series of treatments and tests on its journey from source to tap.
Let’s explore some of the risks associated with drinking contaminated water, and the steps involved in mitigating these risks through our water treatment systems with the help of civil engineers who design them.
Health Risks of Drinking Contaminated Water
Drinking water has the potential to be contaminated at its source as well as within the water distribution system. The EPA is responsible for regulating the quality of the drinking water in the U.S. and sets the maximum allowable levels for concentrations of various contaminants. Some of these are chemicals, organisms and pollutants that lead to dangerous health effects such as neurological disorders, gastrointestinal illness, reproductive issues, and increased risks for illness in people with compromised immune systems. The Centers for Disease Control and Prevention (CDC) ranked the top 10 contaminants in water systems that cause health issues:
- Hepatitis A
- E.coli and excess fluoride (tied)
4 Steps of Community Water Treatment
1. Coagulation and Flocculation
In coagulation, positively charged chemicals such as aluminum sulphate, polyaluminum chloride or ferric sulphate are introduced to the water to neutralize the negative charges held by solids, including dirt, clay, and dissolved organic particles. After neutralizing the charge, slightly larger particles called microflocs are formed from the binding of smaller particles with the added chemicals.
After coagulation, a gentle mixing known as flocculation occurs, causing microflocs to collide with each other and bond together to form visible suspended particles. These particles, called flocs, continue to increase in size with additional mixing and reach an optimum size and strength, preparing them for the next stage in the process.
The second stage takes place when the suspended matter and pathogens settle at the bottom of a container. The longer the water sits undisturbed, the more solids will succumb to gravity and fall to the container floor. Coagulation makes the sedimentation process more effective because it makes the particles larger and heavier, causing them to sink more quickly. For a community water supply, the sedimentation process must happen continuously and in large sedimentation basins. This simple, low-cost application is a necessary pre-treatment step before the filtration and disinfection stages.
At this stage, the floc particles have settled to the bottom of the water supply and the clear water is ready for further treatment. Filtration is necessary due to the small, dissolved particles that are still present in clear water, which include dust, parasites, chemicals, viruses, and bacteria.
In filtration, water passes through physical particles that vary in size and composition. Commonly used materials include sand, gravel, and charcoal. Slow sand filtration has been used for more than 150 years, with a successful record for removing bacteria that causes gastrointestinal disorders. Slow sand filtration combines biological, physical, and chemical processes in a single step. On the other hand, rapid sand filtration is a purely physical purification step. Sophisticated and complex, it is used in developed countries that have sufficient resources for treating large quantities of water. Rapid sand filtration is a cost-intensive method compared to other options, requiring power-operated pumps, regular cleaning, flow control, skilled labor, and continuous energy.
The final stage in the community water treatment process involves adding a disinfectant such as chlorine or chloramine to the water supply. Chlorine has been used since the late 1800s. The type of chlorine used in water treatment is monochloramine. This is different than the type that can harm the indoor air quality around swimming pools. The main effect of the disinfection process is to oxidize and eliminate organic matter, which prevents the spread of parasites, viruses, and bacteria that may remain in the drinking water. Disinfecting also serves to protect the water from germs it may be exposed to during distribution as it is piped to homes, schools, businesses, and other destinations.
Water Systems and Civil Engineers
Civil engineers, the experts responsible for building and repairing infrastructure like water treatment systems, are central to establishing sources of clean water that are safe for residents to use and drink. Water treatment systems designed by civil engineers are a vital component of public health and safety for us all.
For more than a century, Ohio University’s Russ College of Engineering and Technology has been teaching engineers how to create for good – how to engineer a better future with responsible and sustainable design. Learn more about our online Master of Science in Civil Engineering program and master how to effectively supervise, plan, design, construct, and operate the infrastructures essential to connect the modern world.
cdc.gov, “Community Water Treatment”
amwater.com, “Water Treatment”
cdc.gov, “Water-related Diseases and Contaminants in Public Water Systems”
epa.gov, “Information about Public Water Systems”
sswm.info, “Rapid Sand Filtration”
sswm.info, “Slow Sand Filtration”
Monochloramine System Stops Legionella Outbreak at Regional Hospital