Cal. Code of Civil Procedure § 1240.650

(a) Where property has been appropriated to public use by any person other than a public entity, the use thereof by a public entity for the same use or any other public use is a more necessary use than the use to which such property has already been appropriated. (b) Where property has been appropriated to public use by a public entity, the use thereof by the public entity is a more necessary use than any use to which such property might be put by any person other than a public entity. (c) Where property which has been appropriated to a public use is electric, gas, or water public utility property which the public entity intends to put to the same use, the presumption of a more necessary use established by subdivision (a) is a rebuttable presumption affecting the burden of proof, unless the acquiring public entity is a sanitary district exercising the powers of a county water district pursuant to Section 6512.7 of the Health and Safety Code.