Last week's ruling by a federal judge severely limiting the transfer of water from Northern California to local taps is causing another in a periodic wave of calls for more conservation of water in order to … well, to accomplish what isn't exactly clear. Use less water, of course, but to what end?

The reality is that San Diego County is mostly desert and semidesert, with some small patches of alpine climate in the mountains and Mediterranean climate along the coast. For the most part, though, we live in an arid climate in which the majority of the water that sustains modern life for several million people has to be piped in from elsewhere.

Were we forced to live on the amount of fresh water naturally available (as the local Indian communities did in the centuries before the Europeans arrived), then the population that could be supported here would be more on the scale of tens of thousands - clearly, not the millions who live here now.

With other states and northern Mexico now having their own population booms and starting to claim their fair share of the Colorado River water that has long slaked Southern California's thirst, this area is more dependent than ever on the Sacramento-San Joaquin Delta supply currently piped south. But that's the same supply the judge just ordered slashed in order to meet federal environmental laws to save an endangered fish, the delta smelt.

Which leaves us where?

The simple, fun answer is: Stop building more houses.

(We pretty much have done that for now, but that's due more to the crash and burn of the housing market than any sort of environmental or water conservation mandate.)

But recent figures show more people are moving out of Southern California than moving in - meaning that our continuing population growth is native-born. Those are our kids, and they're going to need a place to live someday, too. It's not as simple as simply shutting the door to folks from Iowa, Idaho and Ohio who see the Chargers games on TV mid-December and want to relocate.

So if we are to conserve water, it isn't to help the environment, it's to preserve our ability to provide new housing for the generations to come.

And if we don't want to do so, it won't hurt Midwestern transplant-wannabes, but native-born kids who grew up here.

I sure don't see any easy answers on our water issues.

At some point, should our regional population continue to grow, Southern California will reach its carrying capacity. Whether it's water supply, air quality or other infrastructure issues, there is a limit to the number of people who can live in any one area.

What is worrying is that carrying capacity will be marked by nothing more than unmitigated market forces - that people will begin moving away in droves because our quality of life, economic opportunities or cost of living have spiraled out of control.

Few of us want a Big Brother-style of government dictating who can and can't live here, but at the same time, water being a public commodity, the government is going to decide how much water each of us will get.

Will that mean the end of grass lawns and tropical foliage? Will we each be reduced to a Japanese tea garden or a yard full of cactus?

Tough decisions lie ahead, and neither conservation alone nor a building moratorium will solve them.

- Contact columnist Jim Trageser at (760) 631-6628 or jtrageser@nctimes.com.