Community Water Treatment
Drinking water supplies in the
United States are among the safest in the world. However, even in the U.S.,
drinking water sources can become contaminated, causing sickness and disease
from waterborne germs, such as Cryptosporidium, E. coli,
Hepatitis A, Giardia intestinalis, and other pathogens.
Drinking water sources are subject
to contamination and require appropriate treatment to remove disease-causing
agents. Public drinking water systems use various methods of water treatment to
provide safe drinking water for their communities. Today, the most common steps
in water treatment used by community water systems (mainly surface water
treatment) include:
Coagulation
and Flocculation
Coagulation
and flocculation are often 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.
Sedimentation
During
sedimentation, floc settles to the bottom of the water supply, due to its
weight. This settling process is called sedimentation.
Filtration
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.
Disinfection
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, and
to protect the water from germs when it is piped to homes 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
disinfections by-products, inorganic chemicals, organic chemicals, and
radionuclides. Specialized methods for controlling formation or removing them
can also be part of water treatment. To learn more about the different treatments
for drinking water, see the National Drinking Water Clearinghouse’s Fact
Sheet Series on Drinking Water TreatmentsExternal.
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
webpageExternal. To learn more about the 90+ contaminants EPA regulates and
why, visit EPA’s Drinking Water ContaminantsExternal page.
Water Fluoridation
Community water fluoridation
prevents tooth decay safely and effectively. Water fluoridation has been named
one of 10 great public health achievements of the 20th century 1.
For more information on the fluoridation process and to find details on your
water system’s fluoridation, visit CDC’s Community Water Fluoridation
page.
Consumer Confidence Reports
Every community water supplier must
provide an annual 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.
Household Water Treatment
Even though EPA regulates and sets
standards for public drinking water, many Americans use a home water treatment
unit 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-entryExternal
(NSF). 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.
The most common types of household
water treatment systems consist of:
Filtration
Systems
A water filter is a device which removes impurities from water by means of a
physical barrier, chemical, and/or biological process.
Water
Softeners
A water softener is a device that 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
Systems
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
Disinfection is a physical or chemical process in which pathogenic
microorganisms are deactivated or killed. Examples of chemical disinfectants
are chlorine, chlorine dioxide, and ozone. Examples of physical disinfectants
include ultraviolet light, electronic radiation, and heat.
