IEUA Regional Plant No. 4 - Rancho Cucamonga Wastewater Treatment and Water Recycling Facility

IEUA Regional Plant No. 4 is a wastewater treatment facility located in Rancho Cucamonga, San Bernardino County, California. Operated by the Inland Empire Utilities Agency, it serves a population of about 84,000 residents in the rapidly growing Inland Empire region. The plant is part of a network of regional water recycling facilities that help manage wastewater for communities east of Los Angeles. As a facility in California, the plant operates under the state's stringent Title 22 water recycling regulations and the federal Clean Water Act, which requires NPDES permits for discharges. For a plant serving over 80,000 people, advanced treatment is typical to meet environmental standards and support water reuse. The plant's recycled water is used for irrigation and industrial purposes, reducing demand on imported water supplies. The plant's treated water ultimately flows into the Santa Ana River watershed, which drains to the Pacific Ocean near Huntington Beach. This watershed supports critical habitat for endangered species like the Santa Ana sucker fish and provides water for agriculture and urban areas. The plant's recycling efforts help maintain base flows in the river and reduce nutrient loading to coastal waters.

The plant discharges into the Santa Ana River watershed, which flows through San Bernardino, Riverside, and Orange Counties before reaching the Pacific Ocean at Huntington Beach. This river system supports diverse aquatic life, including the endangered Santa Ana sucker, and provides water for groundwater recharge and agriculture. The arid Southern California climate makes water recycling essential for maintaining stream flows and reducing reliance on imported water from the Colorado River and State Water Project.