The Quartz Hill Water Treatment Plant was the first plant built by the Agency and is also the location of the Agency Headquarters. The main control room monitors the Quartz Hill Plant and all of the Agency's other treatment and distribution facilities. After the completion of the second expansion in 1989, the Quartz Hill Water Treatment Plant became capable of producing 65 million gallons per day (mgd), enough to serve the needs of 280,000 people.

• The treatment plant receives water by gravity from the California Aqueduct.
• Screening and metering are provided at the head of the plant, followed by treatment chemical addition, flash mixing, tapered energy flocculation, clarification utilizing traveling bridges for sediment removal, and dual media filters.
• Treated water is stored in a 9.2 million-gallon reservoir which supplies water by gravity into the distribution system.
• Decanted water from the solids removal process is returned to the plant influent.