Water, according to T.S. Eliot, is "sullen, untamed and intractable, patient to some degree, at first recognized as a frontier; useful, untrustworthy, as a conveyor of commerce; then only a problem confronting the builder of bridges." Water blocks and allows, works with and against, is all things, is necessary, and is almost our bodies.

Water resists irony, perhaps because it flows around all obstacles. Its grandness cannot be diminished; every body of water is conscious of its tiniest parts. Its literary pedigree boasts equal parts nobility and New Age. Think about the language of water, so very many words to express what is, at heart, the very same thing: rain, channel, current, trickle, torrent, sea. Pond, cloudburst, deluge; fountain, river, well.

One of my favorite expressions is "the drink," as in "she stood up drunkenly in the boat and fell into the drink."

The shape of water is the shape of the container, be it basin, bay, or highball glass. So many of the qualities of water are emotions we assign to it, as befits such a mercurial element. The words we use to describe an aquatic surface are all anthropomorphic: calm, choppy, black, frothy, churning, moody. We attach moral value to color and surface, and are instinctively attracted to water that is clean and blue with a clear view to the white sand below. A stretch of muddy water is thought to be sad, even when tinted with natural riverbed silt. A swollen, flooding river is said to be angry, marauding.

The water in Roni Horn's Dictionary of Water is prosaic water, ignored water, water tainted by humans. In this case, it's the River Thames, in 90-plus images photographed over two seasons in 1999. Each portrait shows water and only water, with the very occasional bit of froth, or dirt, or oil slick, or a branch reflected and refracted by waves. It is a project that--perhaps here in book form, rather than in exhibition form--is about intimacy and looking closely. (Although I wondered, if presented with similar portraits of other rivers, would I be able to tell the one from the other? The stinking brown Arno from the toxic East River?) The variation from image to image simply stuns, while the undertow of sameness lulls.

Water, of course, is not blue. It's black, and green/blue, and gray, and vomitously pied, as well as a surprising gold hue that looks like sand. There are all sorts of points between dead calm and breakers, sometimes patterned by rain, other times pockmarked by stones or bird shit. Where was my mind while I leafed through this book? Why did I think that a vague area of color in one image might be a drowned body rising to the surface? What will it look like tomorrow?

Roni Horn, like water, is a fluent artist. Her sculpture is minimalist and material; previous photographic projects include You Are the Weather, a series of 100 portraits of a woman up to her neck in water. One senses in her work a continual refinement of a theme, a shaving away in order to add up. First we look at a body in water, then just at the body of water itself. Then we look at sculptures that look like water. We look and we look.

Water loves a paradox. Years ago, I wandered into an art gallery in New York City where there was an exhibition of photographs by Hiroshi Sugimoto. Each was a black-and-white image of a barren seascape, carefully engineered so that the horizon fell at the same longitude within the frame. Here too, the differences between the images--the direction of the ripples, the shades of gray, the cross-hatching that indicates a gust--at first minute, became more pronounced the longer I looked at them, but the deeper experience lay in the content, and the lack of content; Sugimoto had found a way to convey something at the same time empty and full. It was the closest I had come to understanding what it is about looking at a wide stretch of water that makes one's heart thump. I understood why, when we are looking for answers, we stare for hours at the point where water meets land, where the sublime meets the everyday.