What are Common Municipal Water Treatment Methods?
Waterborne germs, such as Cryptosporidium, E. coli, Hepatitis A, Giardia intestinalis, and other pathogens can contaminate drinking water causing severe illness.
Drinking water sources are subject to contamination and require appropriate treatment to remove disease-causing agents. Public drinking water systems use numerous methods of water treatment to provide safe drinking water for their communities. The most common steps in water treatment used by municipal water systems (mainly surface water treatment) include:
Ultraviolet (UV) rays penetrate harmful pathogens in the water and destroy illness-causing microorganisms by attacking their genetic core (also known as their DNA).
Coagulation and Flocculation
Coagulation and flocculation are frequently the first steps in water treatment. Chemicals with a positive charge are added 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, floc settles to the bottom of the water supply, due to its weight. 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 (for example, chlorine, chloramine) may be added in order to kill any remaining parasites, bacteria, and viruses to protect the water from germs when it is piped to households and businesses.
Water may be treated differently in different communities depending on the quality of the water that enters the treatment plant. Typically, surface water requires more treatment and filtration than ground water because lakes, rivers, and streams contain more sediment and pollutants and are more likely to be contaminated than ground water. Some water supplies may also contain disinfecting by-products, inorganic chemicals, organic chemicals, and radionuclides. Specialized methods for controlling formation or removing them can also be part of water treatment.
Household Water Treatment
Even though the EPA regulates and sets standards for public drinking water, many Americans use home water treatment units to:
Remove specific contaminants
Take extra precautions because a household member has a compromised immune system
Improve the taste of drinking water
Household water treatment systems are composed of two categories: point-of-use and point-of-entry. Point-of-entry systems are typically installed after the water meter and treat most of the water entering a residence. Point-of-use systems are systems that treat water in batches and deliver water to a tap, such as a kitchen or bathroom sink or an auxiliary faucet mounted next to a tap.
There are four common types of household water treatment systems:
A water filter removes impurities from water by means of a physical barrier, chemical, and/or biological process.
A water softener reduces the hardness of the water. A water softener typically uses sodium or potassium ions to replace calcium and magnesium ions, the ions that create “hardness.”
Distillation is a process in which impure water is boiled and the steam is collected and condensed in a separate container, leaving many of the solid contaminants behind.
Disinfection is a physical or chemical process in which pathogenic microorganisms are deactivated or killed. Examples of chemical disinfectants include chlorine, chlorine dioxide, and ozone. Examples of physical disinfectants include ultraviolet light, electronic radiation, and heat.