California Code, Water Code - WAT § 46325

When any tract of land upon which any assessment provided for by this division has been levied is subdivided into smaller parcels the board shall, upon its own motion or upon written application therefor signed by all of the landowners of record within the subdivided tract, reapportion the assessment upon such tract in such manner as will, in the judgment of the board, charge each of the smaller parcels with a just portion of the assessment.  Such reapportionment shall be entered in the minutes of the board and, upon such entry, shall then become final.  If an application for reapportionment is signed by less than all of the landowners within the subdivided tract, or if reapportionment is upon motion of the board, the board may make such reapportionment only after a hearing for which notice to all persons interested shall have been given in the manner prescribed by the board.