California Code, Health and Safety Code - HSC § 116550

(a) No person operating a public water system shall modify, add to or change his or her source of supply or method of treatment of, or change his or her distribution system as authorized by a valid existing permit issued to him or her by the department unless the person first submits an application to the department and receives an amended permit as provided in this chapter authorizing the modification, addition, or change in his or her source of supply or method of treatment.

(b) Unless otherwise directed by the department, changes in distribution systems may be made without the submission of a permit application if the changes comply in all particulars with the waterworks standards.