How is city water treated?

The exact water treatment process may vary slightly from one city to another, but here is a general overview:

1. Intake and Screening: The water source, such as a river, lake, or reservoir, is directed to the water treatment plant through an intake structure. At the intake, screens remove large debris, trash, and fish.

2. Coagulation: Coagulation is the process of destabilizing impurities and particles in the water, making them easier to remove. This is achieved by adding a coagulant, such as alum (aluminum sulfate), to the water. The coagulant reacts with the negatively charged impurities in the water, causing them to neutralize their charges and clump together.

3. Flocculation: Flocculation follows coagulation and promotes the formation of larger, heavier particles called "flocs." Slow-moving basins or tanks are used, allowing the flocs to collide and merge into larger aggregates.

4. Sedimentation: The flocs are then separated from the water by gravity in large settling basins or sedimentation tanks. The flocs settle to the bottom, forming sludge, while the clarified water rises to the top.

5. Filtration: Filtration removes any remaining suspended particles, including fine particles and microorganisms. The water passes through multiple layers of sand or other granular media, which capture the impurities while allowing the filtered water to pass through.

6. Disinfection: Disinfection is a crucial step to eliminate disease-causing microorganisms like bacteria, viruses, and cysts. Chlorine, chloramine, ozone, or ultraviolet (UV) radiation are commonly used for disinfection.

7. pH Adjustment and Corrosion Control: After disinfection, the water's pH level may be adjusted to maintain the desired acidity level and minimize corrosion of pipes and fixtures. Chemicals like sodium hydroxide or lime may be added for pH adjustment.

8. Storage and Distribution: The treated water is then stored in elevated reservoirs or underground storage tanks before being distributed to homes, businesses, and industries through a network of pipes.

Regular monitoring and testing are conducted throughout the water treatment process to ensure the water meets safety and quality standards. As technologies and regulations evolve, additional treatment steps or techniques may be implemented to further enhance the quality of city water.