Cal. Water Code § 60211

No person shall vote at any district election held under the provisions of this act who is not a voter within the meaning of the Elections Code, residing in the division of the district in which he or she casts his or her vote. For the purpose of registering voters who shall be entitled to vote at district elections, the county elections official is authorized, in any county in which there is a district, to indicate upon the affidavit of registration whether the voter is a voter of a district.