• PRETREATMENT - Water drainage from farmlands east of Yuma flows to the plant in a concrete-lined drainage canal. When it enters the plant, the water is filtered through screens that remove algae, sediment and large debris. The water then flows through the plant's underground pipes where it is treated with chlorine to kill microorganisms and prevent algae growth.
• REVERSE OSMOSIS - Up to this point, large particles have been removed from the water, but salt still remains. Fourteen pumps force the water at a high pressure - 362 pounds per inch - through membranes, which separate most of the salt from the water. This process is called reverse osmosis. About 3 percent of the salt still remains in the water, which is why it is further treated with minerals. The desalted water then flows through another concrete-lined canal to the Colorado River, where it is discharged.
• DESALINATION - Reject water, or brine, left behind the membranes during the previous step contains concentrated salts with salinity levels up to 10,000 parts per million. This pressurized reject water is used to power the plant's pumps and help reduce its overall energy consumption. It then flows to the Cienega de Santa Clara at the Gulf of California.
SOURCE: Bureau of Reclamation's Yuma Area Office, www.usbr.gov/lc/yuma