IN WRITING ABOUT WATER, which is second in

importance only to the air we breathe, if, indeed, even that distinction can be made, there are two problems. An abundance of information exists, so the material has to be carefully winnowed, and since it is so ordinary, the subject somehow has to be made exceptional.

Yet the subject is of crucial importance, as both authors tell us in their separate ways. Fred Powledge, in Water, takes us on a Cook's tour of contemporary water quantity and quality issues in this country. William L. Kahrl, in Water and Power, a work of greater historical depth, chose the microcosm; the story told partially in the movie Chinatown of how Los Angeles drained the Owens Valley dry in order that it might prosper.

The lesson is the same in both books: growth, more growth and growth gone awry have hurt some and benefited others in the past, but in future years the depletion of water supplies, and their contamination, will increasingly involve us all. It is not that the faucet will immediately run dry but, more likely, it will run less fully and perhaps there will be a little sickness involved.

Powledge begins with a fascinating description of the properties of water and its amazing statistics. For instance, it is calculated that on the inhabited continents of this world there are 10,037,978,000,000,000 gallons of water available from river runoff--its most common form of capture. Yet not all of this water is in the right place at the right time.

Nowhere is this difficulty better illustrated than in the 17 western states where 84 percent of the nation's water supply is consumed, most of it on arid or semiarid lands used for agriculture. A New Yorker, Powledge is surest on the water problems of the Northeast. He approaches the West as a slightly incredulous, biased visitor.

In fact, bias mars the book in a wider sense. Government bureaucrats and private industry are bad. Conservationists and concerned citizens are good. A pristine river is close to godlike, while a used river is at the other end of the spectrum. This is the hyperbole of the latest conservation movement, and would have been excusable and even somewhat novel 10 years ago.

But we have moved past the black and white stage to recognizing the need for rational discussions and fair solutions to the complex problems inherent in the overuse of natural resources. It is this more mundane approach that Kahrl takes in his tightly focused study of one continuing water war -- a war which has wider implications.

The different approaches of the two writers to the same subject is best illustrated by this example. Powledge refers to the "destructive, wasteful services" of Washington's dam-building bureaucracy. "Like sharks that must devour and rodents that must gnaw, the builders must build or they will become extinct." Too easy, and oversimplified, that analysis. It ignores the very real economic and political pressures that come from these bureaucrats' constituencies, which are a less obvious target.

Summing up after 442 pages of densely packed information, Kahrl, the editor of the innovative California Water Atlas, states, "If there is any lesson to be drawn from the long history of relations between Los Angeles and the Owens Valley, it is that the policies of the (Los Angeles) Department of Water and Power are neither benevolent nor malicious; they are merely practical." The drive to build water projects usually comes down to that hard-to-dramatize fact.

What Los Angeles did to that once lush valley to the north has been part of the mythology of the West for three-quarters of a century. The image of the city, and its surrounding region, as an all-devouring monster gobbling up smaller, more distant prey, derived, in large part, from those events.

The image worked to Los Angeles' detriment last June when, for the first time, southern California lost a bid for a significant amount of additional water from northern California. The politics of panic, which Kahrl traces back nearly a hundred years, were very much in evidence during that election campaign.

There may be more than the average reader may ever want to know about the Owens Valley and Los Angeles water politics in Kahrl's exhaustively researched book, which moves along with the same implacability as Los Angeles' unquenchable thirst, but the compilation of all those facts was needed to dispell the myths.

And the myths about water, especially its eternal abundance, need to be stripped away in a careful and believable manner if lessons are to be learned and solutions found to what has been labeled a water crisis.