Where Does My Drinking Water Come From and How Is It Treated?
In most cases, drinking water comes from two sources. The water that systems pump and treat from sources open to the atmosphere, such as rivers, lakes, and reservoirs is known as surface water. Water pumped from wells drilled into underground aquifers, geologic formations containing water, is called ground water. Large-scale water supply systems tend to rely on surface water resources, while smaller water systems tend to use ground water. Your drinking water comes from the Falls Lake Reservoir located in Northern Wake County. To learn more about Falls Lake and it’s surrounding watershed, please refer to the following web link: www.deh.enr.state.nc.us/pws/swap.
How Does Water Get ToMy Faucet?
An underground network of pipes typically delivers drinking water to the homes and businesses served by the water system. Small systems serving just a handful
of households may be relatively simple, while large metropolitan systems can be extremely complex—sometimes consisting of thousands of miles of pipes serving millions of people. The City of Raleigh for example manages approximately 2,000 miles of water distribution lines which provide water service to over 380,000 people. Drinking water must meet required health standards when it leaves the treatment plant. After treated water leaves the plant, it is monitored within the distribution system to identify and remedy any problems such as water main breaks, pressure variations, or growth of microorganisms.
How Is My Water TreatedTo Make It Safe?
Water utilities throughout the country treat nearly 34 billion gallons of water every day. In fact, during 2006, the City of Raleigh’s E.M. Johnson water treatment plant processed an average of 48 million gallons per day (MGD). The amount and type of treatment applied varies with the source and quality of the water. Generally, surface water systems require more treatment than ground water systems because they are directly exposed to the atmosphere and runoff from rain and melting snow. Water suppliers use a variety of treatment processes to remove contaminants from drinking water. These individual processes can be arranged in a “treatment train” (a series of processes applied in a sequence). The most commonly used processes include coagulation (flocculation and sedimentation), filtration, and disinfection. Some water systems also use oxidation, ion exchange, and adsorption. Water utilities select the treatment combination most appropriate to treat the contaminants found in the source water of that particular system.
Coagulation (Flocculation & Sedimentation):
Flocculation: This step removes dirt and other particles suspended in the water. Alum and iron salts or synthetic organic polymers are added to the water to form tiny sticky particles called “floc,” which attract the dirt particles.
Sedimentation: The flocculated particles then settle naturally out of the water.
Filtration:
Many water treatment facilities use filtration to remove all particles from the water. Those particles include clays and silts, natural organic matter, precipitates from other treatment processes in the facility, iron and manganese, and microorganisms. Filtration clarifies the water and enhances the effectiveness of disinfection.
Disinfection:
Disinfection of drinking water is considered to be one of the major public health advances of the 20th century. Water is often disinfected before it enters the distribution system to ensure that dangerous microbial contaminants are killed. Chlorine, chloramines, chlorinates, or chlorine dioxides are most often used because they are very effective disinfectants, and residual concentrations can be maintained in the water system.
Disinfection Byproducts
Disinfection of drinking water is one of the major public health advances of the 20th century because its practice has eliminated the concern for waterborne diseases such as dysentery, giardia, etc... However, sometimes the disinfectants themselves can react with naturally occurring materials in the water to form unintended byproducts, which may pose long term health risks. EPA recognizes the importance of removing microbial contaminants while simultaneously protecting the public from disinfection byproducts, and has developed regulations to limit the presence of these byproducts. This is why the City of Raleigh began using ferric sulfate, ozone and chloramines in its treatment process and flushing the entire water distribution system once per year in March with free chlorine.
In addition, all sources of drinking water contain some naturally occurring contaminants. At low levels, these residual contaminants are not currently considered harmful in our drinking water. Removing all contaminants would be extremely expensive, and in most cases, would not provide increased protection of public health. A few naturally occurring minerals may actually improve the taste of drinking water and may even have nutritional value at low levels.
Why Is My Water Bill Rising?
The cost of drinking water is rising as suppliers meet the needs of aging infrastructure, comply with public health standards, and provide additional water capacity as water usage per capita increases in most areas and the number of customers served increases. Also, public water systems have previously developed their least expensive water supply sources and developing future supply sources increases construction and operation costs. In most cases, these increasing costs have caused water suppliers to raise their rates. However, despite rate increases, water is generally still a bargain compared to other utilities, such as electricity, cable TV, gas, and phone service. In fact, in the United States, combined water and sewer bills average only about 0.5 percent of household income.
For More Information Contact:
Ed Buchan
Environmental Coordinator - Water
Public Utilities Department
P.O. Box 590
Raleigh, NC 27602
919-857-4540
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