Cal. Wat. Code § 35003.1
A district may, by ordinance adopted at least 90 days prior to any district election, determine that voters shall thereafter be ascertained pursuant to this section.
In that event, the county elections official shall prepare the voter list required by Section 10525 of the Elections Code based upon the last equalized assessment roll of each affected county corrected to reflect, in the case of transfers of land, those persons who as of the 45th day prior to the election appear as owners on the records in the office of the county assessor which the assessor will use to prepare the next ensuing equalized assessment roll and which shall be conclusive evidence of ownership and of the value of land so owned. Where only a portion of a parcel of land has been transferred, and the assessed value thereof and of the remaining parcel are not separately stated upon the roll, estimated assessed values therefor shall be made by the county assessor, and the estimates shall, for the purposes of this section, be considered the value of the land. If more than one person or entity are shown as the owners of record of a parcel of land, the county elections official shall apportion the voting rights between the owners based upon the respective record interests in the information with respect thereto as the county elections official deems correct, proper, and appropriate.
Ca. Water Code § 35003.1