(1) No new public water system shall be approved within a critical water supply service area subsequent to establishment of external boundaries unless specifically authorized by the department. Authorization shall be based upon compliance with the following:

(a) If unanticipated demand for water supply occurs within a purveyor's future service area, the following shall apply in the listed sequence:

(i) The existing purveyor shall provide service in a timely and reasonable manner consistent with state board of health regulations; or

(ii) A new public water system may be developed on a temporary basis. Before authorization, a legal agreement will be required which includes a schedule for the existing purveyor to assume management and/or connect the new public water system to the existing system; or

(iii) A new public water system may be developed. Before authorization, a revised service area agreement establishing the new purveyor's future service area will be required.

(b) If a demand for water supply occurs outside any purveyor's future service area, the following shall apply in the listed sequence:

(i) Those persons anticipating the need for water service shall contact existing nearby purveyors within the critical water supply service area to determine whether any will be interested in expanding their system to provide water service in a timely and reasonable manner consistent with state board of health regulations.

(ii) A new public water system may be developed on a temporary basis. Before authorization, a legal agreement will be required which includes a schedule for an existing system to assume management and/or connect the new public water system to an existing system; or

(iii) A new public water system may be developed.

Any of the options listed in subdivisions (b)(i), (b)(ii), or (b)(iii) will require establishment of new or revised service area agreements.

(2) If a new public water system is developed, it shall have an approved water system plan pursuant to WAC 248-54-580 and the provisions of this chapter. The plan shall include a section addressing the outcome of subsections (1)(a), or (1)(b) along with documented confirmation by the appropriate existing purveyors(s).

(3) Any proposed new public water system shall not be inconsistent with local adopted land use plans, shoreline management programs, and/or development policies as determined by the appropriate county or city legislative authority(ies).

(4) If a coordinated water system plan has been approved for the affected area, all proposed new public water systems shall be consistent with the provisions of that plan.