(1) Each purveyor within the external critical water supply service area boundaries shall be responsible for completion of a water system plan for the purveyor's future service area, including provisions of WAC 248-56-730, if such a plan has not already been approved, with the following exception:

(a) Nonmunicipally owned public water systems shall be exempt from the planning requirements (except for the establishment of service area boundaries pursuant to WAC 248-56-730) if they:

(i) Were in existence as of September 21, 1977; and

(ii) Have no plans for water service beyond their existing service area; and

(iii) Meet minimum state board of health requirements (chapter 248-54 WAC).

(2) Each purveyors' water system plan shall be updated at the time the coordinated water system plan is prepared, which will eliminate the necessity of updating the water system plan prior to the mandatory five year update of the coordinated water system plan.

(3) The content of a water system plan shall be consistent with WAC 248-54-580 and shall comply with guidelines* which may be obtained from the department. These guidelines have been compiled to further assist in meeting the purpose of this chapter, and address three levels of planning requirements varying in detail, based upon the size of the public water system.