Cal. Water Code § 23240

All payments to the United States under any contract between a district and the United States, including payments of interest and principal on bonds deposited with or transferred to the United States, shall be paid, unless otherwise provided by the contract, from revenue derived from annual assessments, apportioned pursuant to this chapter, upon real property within the district assessable for district purposes under the laws of the State, and the real property shall be and remain liable to be assessed and levied upon for the payments.