California Code, Water Code - WAT § 51337

In lieu of completing the operation and maintenance assessment roll, the board may, following each levy of assessment, cause a supplement to be prepared and filed with the county treasurer setting forth the rate and total assessment as determined by the board, and when so filed it shall be deemed a part of the original operation and maintenance assessment roll to the same extent and purpose as if said rate and total assessment had actually been inserted in said original operation and maintenance assessment roll.