Cal. Water Code § 1121

The board shall serve a copy of a decision or order on the parties by personal delivery, certified mail, in accordance with the manner of service of a summons under Article 3 (commencing with Section 415.10) of, and Article 4 (commencing with Section 416.10) of, Chapter 4 of Title 5 of Part 2 of the Code of Civil Procedure, or by any method of physical delivery that provides a receipt. For purposes of this section, “physical delivery that provides a receipt” includes physical delivery methods that provide electronic confirmation of delivery to the intended address.