A May 2025 agreement between Conagua and Baja California calls for seawater intake and brine-discharge works, a conveyance pipeline, the Rosarito storage tank, intake and discharge connections, electrification and electromechanical systems. Conagua is responsible for contracting the plant and most of those works, while Baja California will handle project electrification and distribution infrastructure downstream of the tank.

Mexico’s federal project database estimates the overall development at roughly $666 million. Conagua Director General Efraín Morales López said in January that the added capacity could increase available water for Tijuana and Playas de Rosarito by up to 45%.

The federal-state agreement identifies the Colorado River-Tijuana Aqueduct as the region’s principal water source and describes it as vulnerable to drought and climate variability, with the desalination project intended to strengthen the metropolitan area's water supply.

Baja California state officials have completed the basic engineering, cost-benefit analysis and bid documentation, according to the state’s latest government report. They also have been coordinating with the Federal Electricity Commission on an agreement to occupy land inside the adjacent thermoelectric complex for hydraulic infrastructure and with Mexico’s grid operator, CENACE, on electrical-supply feasibility.

The project’s 2024 environmental filing proposed drawing seawater through infrastructure at the commissin's adjacent Presidente Juárez thermoelectric facility and returning concentrated brine through its discharge system. An earlier design also contemplated an 18-mile aqueduct and estimated that a 50-mgd phase would require about 40 MW. Current documents do not establish whether Cox’s final design retains those specifications.

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The contract followed two unsuccessful procurement rounds. Conagua moved to a restricted international invitation after the earlier tenders failed, ultimately choosing Cox’s offer over bids from Acciona Aguas México and a Tecno Arrendamientos y Construcciones consortium.

Asked in June about the repeated procurement failures, Mexican President Claudia Sheinbaum said bidders had not met technical or financial specifications and called desalination “the only way to provide water to Rosarito and Tijuana,” in remarks translated from Spanish.

The Rosarito project also figures into U.S.-Mexico planning for Tijuana’s wastewater system. Minute 333, a binational sanitation agreement signed in December 2025, requires Mexico to provide U.S. officials with estimates of additional wastewater flows expected from the desalination plant. Those figures are to inform a Tijuana water-infrastructure master plan and systemwide mass-balance analysis and are expected to help determine “potential additional demand on Tijuana’s wastewater treatment capacity,” according to Minute 333.

A binational work group is separately assessing the technical and financial feasibility of expanding the San Antonio de los Buenos wastewater treatment plant from 18.26 mgd to 43.37 mgd. By June, the group had reviewed engineering and financial studies for a possible ocean outfall there and prepared the scope for the systemwide flow analysis, according to the U.S. Environmental Protection Agency. Officials of the International Boundary and Water Commission, United States and Mexico, told ENR they could not respond to questions about projected Rosarito wastewater flows before publication.

US Commission Asks Mexico to Prioritize Pipes Leaking Raw Sewage in Tijuana River Valley

That work is proceeding alongside a broader construction program on both sides of the border. The U.S. is expanding the South Bay International Wastewater Treatment Plant toward 50 mgd, while Mexico is rehabilitating collectors, interceptors and pumping facilities. Early work and procurement of long-lead equipment are underway at the plant, and five Mexican sewer and pump-station rehabilitation projects were in construction or procurement as of June, EPA said.

Failures have continued during the broader infrastructure buildout. ENR reported that two sections of Tijuana’s Parallel Gravity Line ruptured within about two weeks in May, at times sending more than 40 mgd to South Bay during emergency repairs. Tijuana’s International Collector is also being rehabilitated and replaced, with the new system designed to carry up to 60 mgd of wastewater and sludge to treatment facilities on both sides of the border.