Cal. Wat. Code § 1005.1
Cessation of or reduction in the extraction of ground water by the owner of a right to extract, as the result of the use of an alternate supply of water from a nontributary source, shall be and is deemed equivalent to, and for purposes of establishing and maintaining any right to extract the ground water shall be construed to constitute, a reasonable beneficial use of the ground water to the extent and in the amount that water from the alternate source is applied to reasonable beneficial use, not exceeding, however, the amount of such reduction. Any such user of water from an alternate nontributary source who seeks the benefit of this section, shall file with the board, on or before December 31st of each calendar year, a statement of the amount of water from such source so applied to reasonable beneficial use pursuant to the provisions of this section during the next preceding water year (November 1st to October 31st), and such user cannot claim the benefit of this section for any water year for which such statement is not so filed.
"Ground water," for the purpose of this section and of Sections 1005.2 and 1005.4, means water beneath the surface of the ground, whether or not flowing through known and definite channels.
The term "nontributary source," as used in this section, shall be deemed to include water imported from another watershed, or water conserved and saved in the watershed by a water conservation plan or works without which such water of the same watershed would have wasted, or would not have reached the underground source of supply of the owner relying upon this section.
Ca. Water Code § 1005.1