Our Water Treatment Process

Photo of Water Treatment Facility

The City's Public Utilities Department provides high-quality drinking water byutilizing proven technology, updated facilities, and state-certified operators.Water is treated at the City's three treatment plants using several processes,with each process providing additional water quality improvements. Usingseveral treatment processes provides multiple barriers for added safety.

Conventional water treatment consists of coagulation, flocculation,sedimentation, and sand/multi-media filtration. Utilizing tried and testedconventional processes offers many advantages, some of which are: extensiveknowledge of the processes, proven performance, cost-effective operation,and acceptance by regulators. Combined with the conventional treatmentprocess, advanced disinfection has been added to the treatment plants.

The Water Treatment Processes We Use Are

Watershed protection: San Diego receives water from local raincollected in City reservoirs and from imported water. Imported watercomprises 85 to 90 percent of our water and travels hundreds of milesbefore reaching our water treatment plants. Protecting the watershedsprevents contamination of our water supply and is the most costeffective process in water treatment. Extensive measures are beingtaken to prevent contamination of our local and imported water.So when you see â??No Swimmingâ? or "No Dumping" near water supplieswe hope you understand this is for the protection of your drinking water.

Coagulation: This is the chemical process of rapidly mixing coagulantsto the water coming into the water treatment plant (source water).Many of the particles in the source water have negative charges causingthem to repel each other, much like two magnets when the negative endsare put together. Coagulation changes the negative charges to neutral.

Flocculation: Coagulated water is slowly mixed causing the neutral particles to collide. When the collisions occur the particles clump together forming floc. As the floc is formed, particles in the water are trappedwithin the floc. The floc now looks like snowflakes suspended in the water.

Sedimentation: The floc particles are heavier than water. Mixing is stopped and the water is allowed to slowly flow through the sedimentationbasins. The floc settles to the bottom and is removed. The clear water iscollected from the top of the sedimentation basins and sent to the filters.

Filtration: Water is passed through deep filtration beds to produce water that is crystal clear. Extremely small particles are removed during this process. San Diego's water treatment plants produce water with turbidities(cloudiness) significantly better than drinking water standards.

Disinfection, Primary: Drinking water is further treated to remove or inactivate viruses, bacteria, and other pathogenic organisms. Disinfection is accomplished in a variety of methods. The Alvarado and Miramar Water Treatment Plants use ozone as the primary disinfectant. The Otay WaterTreatment Plant uses chlorine dioxide as the primary disinfectant. These areadvanced disinfection processes and have the advantage of providing higherquality water with better taste.

Disinfection, Secondary: Chloramines are created by adding chlorine and ammonia to the water as the last step in the treatment process.Chloramines help prevent microbial contamination from occurring in thewater distribution system.

Corrosion Control: The corrosivity of the water is controlled by adjusting the pH.

Graphic of Water Filtration Process, Reservoir, Coagulation, Flocculation/Sedimentation, Filtration, Treated Water Storage