Local water comes from the wells YLWD operates within one mile of our headquarters. The District’s wells tap an underground aquifer that underlies most of northern Orange County known as the Orange County Groundwater Basin.
The aquifer is carefully managed by the Orange County Water District (OCWD) and is replenished by water from the Santa Ana River, local rainfall, and surplus water purchased from imported sources. The basin, itself, began forming millions of years ago as mountains eroded and ocean sediments filled a deep valley, trapping Santa Ana River water between the layers of accumulated sand and gravel. It holds between 10 million and 40 million acre-feet of water, of which 1.25 million to 1.5 million acre-feet, or approximately half a billion gallons, is usable. OCWD allows more than 20 cities and water agencies, including YLWD, to withdraw water from the basin, via wells. Even for agencies that have access to the groundwater basin, there is a maximum percentage of water that can be pumped. In the past few years, that number has been between 77% and 85% of an agency’s total water portfolio.
Nearly one-third of all wastewater in Orange County is treated to recharge the aquifers. The OCWD Groundwater Replenishment System is a purification process that treats wastewater with one of the most advanced water purification processes in the world using microfiltration, reverse osmosis, and ultraviolet light with hydrogen peroxide. The near-distilled quality water is then pumped to percolation ponds that replenish Orange County Water District’s groundwater basin.
In 2023, approximately 11% of Yorba Linda Water District’s drinking water was purchased from the local wholesaler, Municipal Water District of Orange County (MWDOC). MWDOC obtains water from the regional supplier Metropolitan Water District of Southern California (MWD). MWDOC then delivers this water to its own 28 client agencies throughout Orange County, including YLWD, which provides retail water services to the public.
This water, known as “imported water”, comes from the Colorado River via the Colorado River Aqueduct and from Northern California via the State Water Project.
MWD owns and operates the Robert B. Diemer Water Treatment Plant located just north of western Yorba Linda where the imported water is treated to meet drinking water standards.
The cost of imported water to the retail agencies, such as YLWD, is almost four times the cost of pumping out of the groundwater basin.
The Colorado River Aqueduct brings water 240 miles through deserts and mountains to its main reservoir, Lake Mathews, in Riverside County where it is distributed to multiple local communities. Originally built to ensure a steady supply of water to Los Angeles, it now serves southern California communities from Ventura County to San Diego County. The construction of the Colorado River Aqueduct is widely credited as being a principal reason for the industrial growth of the four counties during World War II and the following decades. In 1992, the Aqueduct was recognized by the American Society of Civil Engineers (ASCE) as one of the seven “wonders” of the American engineering world.
The State Water Project, also known as the California Aqueduct, transports water 600 miles from Northern California and the Sacramento-San Joaquin Delta. This aqueduct system is owned and operated by the State of California and is the longest aqueduct in the world. It is comprised of 23 dams and reservoirs, 22 pumping stations, 473 miles of canals, 175 miles of pipeline, and 20 miles of tunnels.
