Furthering efforts to improve resilience and protect drinking water supplies threatened by climate change impacts, the San Diego Regional Water Quality Control Board for the first time has authorized the use of advanced treated recycled wastewater to replenish groundwater. 

The permit approved by the San Diego Water Board allows Pure Water Oceanside to inject up to 3 mgd of highly treated water from its Advanced Water Purification Facility into the San Luis Rey Hydrologic Unit, where the recycled water will commingle with naturally occurring groundwater. Six months later, the water will be extracted from the aquifer and undergo final treatment at the Mission Basin Groundwater Purification Facility before being distributed throughout the region as drinking water. 

“This is a major development for Oceanside and a region that imports about 90% of its water,” says Board Chair Celeste Cantu. “With climate change contributing to decreased snowpacks in California and the Colorado River Basin and exacerbating our water supply and reliability issues, our board strongly supports the use of advanced treated recycled wastewater as a safe, reliable supplement to traditional sources that will help us better prepare for a very uncertain climate future.”

In addition to increasing reliability and promoting drought resilience, the new water source will help lower overall treatment costs and capture an estimated 4.5 million gallons of treated wastewater — 1.5 million of which will be used for agricultural operations — that otherwise would be discharged into the ocean. 

Pure Water Oceanside is similar to other advanced treatment projects operating or being implemented throughout California, among them Orange County’s Groundwater Replenishment Project, Pure Water Monterey and Pure Water Soquel in Santa Cruz. The technology utilizes advanced water treatment processes of ultrafiltration, reverse osmosis and advanced oxidation with ultraviolet light to produce water that meets state and federal standards and is of safe, near-distilled, purified water quality.

The permit is consistent with the goals of the “Strategize to Achieve Resilient Local Water Supply” chapter of the board’s Practical Vision. 

The San Diego Water Board’s region covers 85 miles of coastline from Laguna Beach to the Mexican border and extends 50 miles inland to the crest of the coastal mountain range. The growing population enjoys a mild climate that is conducive to many water-related activities. However, because the area receives little precipitation, approximately 90% of its water supply is imported from Northern California and the Colorado River.