Insofar as the commission on water resource management, as the agency authorized to administer the state water code, determines the contents of the Hawaii water plan, which includes the designation of hydrologic units and sustainable yields, and the commission's "interpretation of its own rules is entitled to deference unless it is plainly erroneous or inconsistent with the underlying legislative purpose", it is within the commission's authority to limit reservations of water to specific aquifers. 103 H. 401, 83 P.3d 664.