Cal. Water Code § 71688

The district, after the levying of the replenishment assessment, shall give notice thereof to the operators of all water-producing facilities in the district as disclosed by the records of such district, which notice shall state the rate of replenishment assessment for each acre-foot of ground water to be produced during the ensuing fiscal year. The notice may be sent by postal card or by other first-class mail with postage prepaid by the district.