The state Water Commission's decision to hold a "buffer" of Waiahole Ditch water in reserve for unspecified future Leeward uses departs from the water code and may not hold up in court.

The commission, which recently issued its decision on allocating the Ko'olau ditch water, has the unenviable task of managing a precious resource that, without competent oversight, could become threatened to the point of chronic shortages. It presents a difficult balance between competing demands, and the notion of an escape hatch — 2.43 million gallons set aside for a Central O'ahu agricultural purpose to be named later — is tempting.

But its decision to allocate that water for future diversion is shortsighted, especially given the lack of permanent stream-flow standards.

The dissenting opinion has a better approach: Keep the flow from the Waiahole Ditch in Windward streams and re-evaluate when an applicant makes a specific proposal. To create an escape clause in the law sets bad precedent for other cases, such as efforts by Maui County to reinvigorate streams that formerly were diverted for agricultural use.

Granted, this particular buffer allotment is only a small percentage of the 27 million gallons a day that flows from the ditch. But authorizing it this time may make it easier to carve off increasingly fat margins in the future.

Dissenters cite an earlier Supreme Court ruling that blocks a previous move by the commission to create a "nonpermitted ground water buffer" to satisfy future permit applications. "Nothing in the code," the court wrote, "authorizes such a measure." That said, it's difficult to see the point of this attempt.

The dissenting opinion, written by state Land Board Chairman Peter Young and state Health Director Chiyome Fukino, correctly faults the majority for allowing some allotments uncritically. The key example: a daily allocation of 750,000 gallons for the Pu'u Makakilo golf course project — for which there are no current development plans — seems ill-founded. While the high court's repeated rejections of this allotment undercut those plans, there's no reason to give water to an inactive golf course project.

The bottom line: The Water Commission should focus on refining what are now interim stream-flow standards to create a more scientific benchmark for evaluating future proposals on how Waiahole water is to be used. Otherwise, the sustainability of stream environments, and everything that arises from them, will be left defenseless in the face of environmental pressures.

To do less also ignores the intrinsic value of keeping stream flow at a healthy level. Without it, Windward O'ahu aquatic and marine life, as well as the agricultural productivity of that side of the island, may never recoup its former potential.