Cal. Water Code § 13999.18

Notwithstanding any other provision of this chapter, and as approved by the Legislature, the board may share in the cost of the construction of treatment works under subdivision (b) of Section 510 of the Federal Water Quality Act of 1987. That participation may be approved only if the board determines that treatment works in Mexico, in conjunction with any defensive treatment works constructed under the Federal Water Pollution Control Act, are not sufficient to protect the residents of the City of San Diego and surrounding areas, including Imperial County, from water pollution originating in Mexico. No project in which the board participates shall receive more than ten million dollars ($10,000,000) in loan proceeds from the board.