It would be a ground-breaking project for Baja California, the largest desalination plant in the Western Hemisphere, situated on the Pacific Ocean in a corner of Rosarito Beach — and could one day serve as a supply for water consumers in San Diego County as well.

But as a critical deadline approaches, two partners in the group that proposed the 100 million-gallon-a-day facility are bitterly at odds, suing each other in U.S. and Mexican courts.