As California contemplates its water future, one simple principle should guide its choices: Any 30-year investment in water infrastructure must take into account what California's water supply situation will be 30 years from now. If population and warming forecasts are correct, by mid-century our state will be more crowded and precipitation patterns will have changed. Some regions may be wetter; most are likely to be drier. No matter what investments we make, water supplies from Northern California and the Colorado River will continue to diminish. More people will chase less water.

That reality is inescapable and makes long-term investment necessary, either this year or soon. Gov. Arnold Schwarzenegger believes that this is the right time to ask voters to approve a $9.3-billion water bond, notwithstanding the state's other pressing needs. He may or may not be right about the timing, but he's certainly correct that we'll have to spend to adapt to a difficult future.

As such, California should invest in projects that encourage everyone to get real -- to acknowledge that water is a scarce resource. Such projects would include investment in local, renewable sources, much like the water-supply action plan that Los Angeles Mayor Antonio Villaraigosa laid out in May. The state should invest to encourage cities to recycle water for potable and nonpotable reuse; to capture rainwater that today flows to the ocean; and to rebuild hardscapes to minimize runoff pollution and allow water to filter into underground aquifers.

California should invest to clean its groundwater in places such as the San Fernando and San Gabriel valleys, where industrial pollutants threaten wells, and in other parts of the state. In addition to boosting local water supplies, cleaning aquifers would provide new underground storage where California might collectwater in wet years for use when times are dry. Underground storage can serve the same purpose as large dams and reservoirs, but with less environmental impact and at lower cost. The state also should invest in plumbing that would allow regions to work together creatively to makesensible and judicious water transfers between communities with sufficient supplies and those without.

Happily, the proposal outlined by the governor last week allows for significant investment in these kinds of projects. We were heartened to see, as well, that Schwarzenegger seems to have dropped a request from a previous bond proposal to designate $5.1billion for several dams that would have primarily benefited agricultural interests in the Central Valley (though at least $3 billion in the proposed new bond could still be used for these projects).

Still, no bond by itself can be a "comprehensive" fix for California's water woes -- and the state can continue working toward its water-use goals whether or not a bond is on the ballot in November. We can continue to address the deterioration of the Sacramento-San Joaquin River Delta -- a major choke point in the state's water supply. Although passing a bond might help fix the delta, a report released Thursday by the Public Policy Institute of California suggests that the ultimate solution may be the construction of a peripheral canal (and the establishment of new forms of governance to make sure that such a canal is operated responsibly). A canal would not be funded by the proposed water bond.

And bond or no bond, California can continue enacting laws that discourage water waste. The Legislature must, for instance, work to perfect AB 2175, a groundbreaking bill that seeks to require Californians to cut per-capita water use by 20% by 2020. California voters might not be up for approving a bond -- even if it's a good bond. That doesn't mean giving up on our state's water challenges.