WATER IS SUCH STRANGE STUFF—so ubiquitous we hardly see it. It might as well be invisible, like one of those weightless fluids that followed Newton into the Age of Reason: phlogiston, caloric, the luminiferous ether, all transparent and aflutter with light. I walk on any ocean beach and the sea takes me in, almost as a friend, a fellow creature, a member of the living clan of shapes and sizes and movement that stretches hopelessly deep into its profligate past. We seem to know one another, this sea and I. I enter, and it subsumes me into itself. I suppose I am nothing more than a thin jelly, a flood of cells, water sluicing in veins and pipes, nothing it has not seen before. It cannot distinguish where I begin and it leaves off. It senses me only as one of its own.

      Indeed, we are watery reeds in a watery world. So much water bound in watery sacks. Even our minds and our very breath rise and fall on the watery tide: eighty percent of our brains and our lungs, sixty-five percent of our entire bodies. Water courses through us, bathes each cell. The moon tugs at these inner seas.

      The Earth, too, is irrigated by water: seventy-one percent of its surface, 320 million cubic miles of it. And there is nearly half this much tied up as “water of hydration,” bound to the ions of solids in the Earth’s crust. An invisible sea. Once you leave Los Angeles on this journey south to the Pole, there is nothing but water—all the way to Antarctica. Perhaps there are a few brown island stones, as smooth as skulls down there, rising above the waves. But even the twin islands of New Zealand seem little more than Maori canoes in the vast Pacific. Beyond Christchurch there is nothing to speak of either but water, until you cross over Wilkes Land and Cape Adare and encounter … yes, more water, though now in the form of Antarctic ice, as far in every direction as the eye can see. (Stephen Pyne has said of “Greater Antarctica” that this is “a world derived from a single substance—water.”) Twenty hours aloft over the Pacific and you get some sense of what the surface Earth is really all about. Solid Ohio, with its browns and greens, its pastures and fences, seems little more than a cartographer’s fiction of soils, plants, and trees. From the observatories of space, from the dry moon itself, it is the signature and brushstroke of water that you see, a delicate blue wash across the Earth.

      Most of this water is in the sea, of course, mixed there with the weathered salts of the continents as churning brine. The remaining fraction is fresh, but most of this is sequestered in ice caps, hoarded there by darkness and cold. What is not stored at the Poles occupies the more familiar niches of lakes and rivers, atmosphere and groundwater. The Antarctic ice cap alone is so vast a storehouse of water that if melted, it would charge the rivers of the world for more than eight hundred years. And the Gulf Stream, wide and sluggish, bringing improbable springtime flowers to fogbound New England coasts, carries in its flow twenty-five times as much water as all the Amazons, Congos, and Mississippis on Earth. When these numbers are taken in and sorted out, it would seem that the hydrosphere—the realm of water in all of its pooled and dropleted and vaporous and streaming forms—was prepared and apportioned more for pilot whales and penguins, anemones and seals, than for those of us who dwell upon land. “Make no mistake,” Varner once said, “water is ubiquitous and yet it is more precious than gold.”

      And more magical. There is a delicacy and power to this fluid that rushes through our veins and our lives, that punctuates waking and dream with longing, whose pools are light among blowing sand, among dark forests and low hills, whose forms—solid, liquid, vapor—are legion. I remember the snows of Pittsburgh, how the flakes grew as they fell, how they thickened and slowed in the viscous air, how they built dangerously on the rooftops until the roofs creaked and bowed under the weight, how mountains broke and avalanched under the winter trees. Or much later, how the waves, bottle green, curled luminous and lifting over the coral shore. How I went down and could not come up under their load. Water is mass and power: its drop-by-drop accretion into flood, its sudden rush through the breached levee, the brown swarm of its carried silt whispering through the drowned corn.

      Once, when the trees of Ohio were silver in morning, they spoke under the gentlest breeze, the clatter of their thin branches ice-cumbered and dazzling, red and green and blue, the spectrum laid out in winter sun. Whole trees with leaves of ice. Whole orchards ablaze in refracted light. When ice forms on a lake, the crystals shoot outward from the cold shore into the center, long fingers extended into pale November afternoons. Dew fixes on the surface of grass, beads in translucent spheres and shakes its silver skin. In the mountains of Montana they said three feet of snow had dropped in a single night. The trains stopped, the cars stopped, the passengers forgot time in rustic inns, sipped hot drinks by the window. The wide streets beyond the parted curtains became legends. Once in Arizona they said the dam might break, so much rain had fallen. Cloudburst after cloudburst. The whole town emptied, the cars moving slowly in lighted procession to high, safe ground. There were just a few of us left on the bar stools, singing, hiding our fear in drink and laughter. But the next day when I awakened there was sun. The waters had flowed off into the night, peaceful and calm, rolling away through the hot desert down to the sea. Skiing on the Great Divide, I saw my daughter Kate stop and shake snow from her left hand. “To the Pacific,” she said, laughing. And from her right hand: “To the Atlantic.” A great smile lit her face.

      Water is everywhere, we just need to remember it. It is in the trees—hundreds of liters transpire each day from an ordinary elm, heaved as gentle fog into the sky. There are a billion billion molecules in a single flake of snow, which is why the great photographer W. A. Bentley, the “snowflake man,” could say that in forty-five years he had never seen two alike. And never would. Water is imbibed in the germination of seeds, a process that involves the uptake of water molecules by coils of cellulose and loops of starch. This “drinking in” can unleash tremendous forces; thus small seeds split rocks weighing tons. Water imbibed by wood can create a force a thousand times atmospheric pressure, which is why the Egyptians used wetted stakes to split limestone for the Pyramids.

      The early Greeks thought that water was not only everywhere, it was everything: every material object, every stone and cloud, every citizen of Crete, was nothing more than water transformed. One substance per world. What economy! Thales of Miletus asked, “What is it that changes, what is it that lies beneath all that we see and feel.” Things come and go, wind turning to rain, rain to earth, earth to sea, the cycles