Water Production
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Department of Public Services
THE TREATMENT PROCESS
 | Water treatment is the process of purifying water, thereby making the water safe to drink. Because it is a good solvent, water picks up all sorts of natural pollutants, and most water found in nature is unsafe 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 upon whose shoulders rest the responsibility for safely and successfully treating the water supply for the City of Lewisville. All operators at the Lewisville Water Treatment Plant are certified and licensed by the Texas Commission on Environmental Quality, ensuring the water that reaches your home meets or exceeds current U.S. Government Standards. The monitoring being done here by a certified operator is performed twenty-four hours a day, seven days a week, three hundred sixty-five days a year. |
| Intake: Raw (untreated) water is pumped from Lewisville Lake through six turbine pumps mounted on a piered intake structure. The intake structure is located near Lewisville Lake. The quality of the raw water is fairly stable throughout the year. The average turbidity, or a measurement of how clear the water is, is 8.5 NTU with a pH and alkalinity of 8.0 and 100, respectively. Activated carbon is used at the intake structure from June through September to aid in the control of taste and odor associated with algae bloom in the warm summer months. | |
| New Intake: The City of Lewisville, through a joint project with the Upper Trinity Regional Water District, is nearing completion of a new raw water intake structure located east of the existing intake. In addition to the intake, a new 36-inch raw water transmission line has been constructed and should be placed into service prior to the spring of 2002. | |
Chemical Addition: Chlorine, ammonia, liquid ferric sulfate, lime, and polymer are added to the water. The water and chemicals are mixed together to start the purification process. Chlorine and ammonia combine to form chloramine, which is a disinfectant. Ferric sulfate, together with lime, serves as coagulants. The polymer is a filter aid. These chemicals kill germs, improve taste, remove odor and help to settle solids. A small amount of fluoride is added after the treatment process to aid in the prevention of tooth decay.
Coagulation and Flocculation: Ferric sulfate and other chemicals cling to foreign matter and particles dissolved in the water. This process is called coagulation. It 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 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 basin, the water flows through filters. Filters are made of layers of gravel, sand and anthracite coal. The filters are used to remove any particles remaining 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 water flows into a ground storage reservoir called a clearwell. This allows time for the chlorine and ammonia to mix through out the water so disinfection can occur. 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 one of the City’s four elevated storage tanks (water towers). These tanks are used to provide additional storage capacity for fire protection, high usage periods, and to maintain and stabilize the pressure in the distribution system. The four elevated tanks have a combined capacity of 6.5 million gallons of drinking water.
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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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