Cal. Water Code § 51383

When an assessment levied for reclamation purposes upon district lands is adjudged invalid as a whole or as to any parcel upon which it was levied, and any landowner has paid any portion of the amount assessed on any parcel before the assessment was adjudged invalid, the amount paid by the landowner with legal interest thereon from the date of such payment shall be credited by the treasurer of the county where the assessment list is filed on any subsequent assessment on the parcel on which the invalid assessment was paid.