Cal. Health & Saf. Code § 4603
This chapter does not affect any other law under which improvements may be made within or by any city but it provides an alternate system of proceedings for sewer work or improvement. Improvements may be made either pursuant to this chapter, or pursuant to any other law. If, however, any proceedings are commenced pursuant to this chapter, its provisions apply to any improvement made under those proceedings until such improvement is completed.
If, after an improvement has been made pursuant to this chapter, the governing body of any city determines that it is necessary or convenient to make any additional improvement, the governing body may proceed to do so either pursuant to this chapter or under any other appropriate law. If the additional improvement is made pursuant to this chapter for the same district, the procedure shall be the same as that which is provided under this chapter for the making of the initial improvement. It is not necessary to reform the district if the governing body finds, following the hearing which is provided for by Section 4611 that the additional improvement is of benefit to the entire district which was previously formed under this chapter as such district is then constituted. As an alternative method, the governing body may make such additional improvement by forming a new district pursuant to this chapter which may include, in whole or in part, territory which is included in any district previously formed pursuant to this chapter.
Ca. Health and Saf. Code § 4603