Cal. EVID § 912

(a) Except as otherwise provided in this section, the right of any person to claim a privilege provided by Section 954 (lawyer-client privilege), 966 (lawyer referral service-client privilege), 980 (privilege for confidential marital communications), 994 (physician-patient privilege), 1014 (psychotherapist-patient privilege), 1033 (privilege of penitent), 1034 (privilege of clergy member), 1035.8 (sexual assault counselor-victim privilege), 1037.5 (domestic violence counselor-victim privilege), or 1038 (human trafficking caseworker-victim privilege) is waived with respect to a communication protected by the privilege if any holder of the privilege, without coercion, has disclosed a significant part of the communication or has consented to disclosure made by anyone. Consent to disclosure is manifested by any statement or other conduct of the holder of the privilege indicating consent to the disclosure, including failure to claim the privilege in any proceeding in which the holder has legal standing and the opportunity to claim the privilege.

(b) Where two or more persons are joint holders of a privilege provided by Section 954 (lawyer-client privilege), 966 (lawyer referral service-client privilege), 994 (physician-patient privilege), 1014 (psychotherapist-patient privilege), 1035.8 (sexual assault counselor-victim privilege), 1037.5 (domestic violence counselor-victim privilege), or 1038 (human trafficking caseworker-victim privilege), a waiver of the right of a particular joint holder of the privilege to claim the privilege does not affect the right of another joint holder to claim the privilege. In the case of the privilege provided by Section 980 (privilege for confidential marital communications), a waiver of the right of one spouse to claim the privilege does not affect the right of the other spouse to claim the privilege.

(c) A disclosure that is itself privileged is not a waiver of any privilege.

(d) A disclosure in confidence of a communication that is protected by a privilege provided by Section 954 (lawyer-client privilege), 966 (lawyer referral service-client privilege), 994 (physician-patient privilege), 1014 (psychotherapist-patient privilege), 1035.8 (sexual assault counselor-victim privilege), 1037.5 (domestic violence counselor-victim privilege), or 1038 (human trafficking caseworker-victim privilege), when disclosure is reasonably necessary for the accomplishment of the purpose for which the lawyer, lawyer referral service, physician, psychotherapist, sexual assault counselor, domestic violence counselor, or human trafficking caseworker was consulted, is not a waiver of the privilege.