Water Production
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Department of Public Services
THE TREATMENT PROCESS
 | Water treatment is the process of purifying water. Treatment makes the water safe to drink. Because it is a good solvent, water picks up all sorts of natural pollutants. In nature, water is not always clean enough for people to drink. Today almost every city in the world treats their drinking water. |
 | In the state of Texas, current rules and regulations have accelerated the need for more competent, skilled water utility operators who are responsible for safely and successfully producing water quality among the safest in the world. All operators at the City of Lewisville Plant are certified and licensed by the Texas Commission on Environmental Quality (TCEQ), ensuring the water that reaches your home meets or exceeds current regulatory standards, at all times.
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| Intake: Water is taken from Lewisville Lake by the use of pumps and delivered to the treatment plant. The City of Lewisville purchases raw (lake) water from the City of Dallas. During the summer months, activated carbon is added to assist in the control of any taste and odor problems. | |
Chemical Addition: Liquid ferric sulfate, lime, polymer, chlorine, and ammonia are added to the water. The water and chemicals are mixed together to start the purification process. These chemicals kill germs, improve taste and odor, and help settle solids.
Coagulation and Flocculation: In the process of coagulation, ferric sulfate and other chemicals cling to particles in the water. This causes the particles to stick together and form larger particles called floc.
 | Sedimentation: The water and floc particles flow into a sedimentation basin. The floc then settles to the bottom and is removed from the purified water. A certified operator is seen taking a sample of the water in the sedimentation basin. The operators perform 2,065 process control tests in their on-site laboratory each week.
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Filtration: From the sedimentation basins, the water flows through filters. Filters consist of 44 inches of anthracite coal. The filters are used to remove any remaining particles left in the water.
Disinfection: A small amount of chlorine and ammonia is added to kill any remaining bacteria and to keep the water safe as it travels through the distribution lines to the public.
Storage: The treated water flows into a ground storage reservoir called a clearwell. This allows time for the chlorine and ammonia to mix through in the water for proper disinfection to take place. The reservoirs also provide a reserve supply of water for high usage periods. The City of Lewisville has three clearwells with a combined capacity of five million gallons.
The water is then pumped into the distribution system lines and the elevated storage tanks. Elevated storage tanks have a two-fold purpose: to provide additional storage and to supply adequate pressure to the distribution system.
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In mid-July the City’s water system was divided into two separate pressure zones to compensate for variations in elevations in the northwest section of the city. This will help to both stabilize and increase pressure. This was accomplished through the completion of a 13.8 MGD pump station located at the Water Treatment Plant and a 2 MG elevated storage tank.
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 | A Motorola System Control and Data Acquisition (SCADA) system monitors the water levels in each tank, as well as the status of the entire distribution system. A certified operator records the water levels in each overhead tank. The operators can also control the rate at which water is being pumped at pump stations throughout the city, as well as all valves in the overhead storage tanks, allowing for even distribution and level control. Problems in the system can easily be detected as the SCADA System records sudden drops in water pressure or unusually high water usage. |
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