Water

Water is the most used substance on earth and, in itself, very nearly worthless. It is heavy, bulky, and free wherever it falls, which means that what is bought and sold is never the substance but access to it at a particular place and time: an allotment from a canal, a share in a company, a connection to a main, a tanker delivery, a bottle. The price of water is almost entirely the cost of moving, storing, and treating it. The scarcity is real nonetheless, because only about 2.5 percent of the planet's water is fresh and nearly all of that is locked in ice or underground — so a substance covering most of the surface of the world is, in the form anyone can use, in short supply.

That is why this category begins with irrigation rather than with drinking. Water becomes a commodity at the moment it has to be allotted: when a canal commands more land than its flow will serve, somebody must decide whose field goes dry, and that decision is the thing of value. Mesopotamian and Egyptian irrigation from around 6000 BCE is the first system to manufacture scarcity in an abundant substance by concentrating demand on a channel, and the instruments appear with it — the measured turn, the canal share, the obligation to maintain a ditch in exchange for a portion of what runs through it. This places water in a small family on this list alongside land and emissions allowances: commodities that had to be defined into existence by a legal instrument before they could be sold at all.

The later forms are variations on the same structure. Urban supply became a traded good through aqueducts whose rights were sold, then through chartered water companies, then through municipal works financed on the strength of their revenues. Industrial process and cooling water is bought by volume. Statutory water markets in the American West and in Australia trade the allotment itself as an instrument divorced from any particular field. And most water that crosses a border does so inside something else, as the volume embodied in a traded crop, which is a trade in water that no customs schedule records.
One historical form deserves separate mention because it is this category's economics in their purest expression: water sold as a solid. Frederic Tudor's first cargo of pond ice reached Martinique in 1806 and melted for want of an icehouse to put it in; Nathaniel Wyeth's horse-drawn cutters in the 1820s made the business profitable; and by 1847, 353 ice-laden vessels cleared Boston Harbor carrying almost seventy-five thousand tons to the American South, to Rio de Janeiro, and to Hong Kong, much of it cut from Fresh Pond in Cambridge. Nothing was manufactured and nothing was added. The entire value was harvest, insulation, and speed, and mechanical refrigeration ended the trade in the early twentieth century. Natural ice belongs here: it is water, carried.

The boundaries run against four neighbors. Hydroelectricity is electric power, while the water right behind the dam and the flow turning a mill wheel are here. Carbonated and flavored bottled beverages are soft drinks; still bottled water is here. Beer, wine, and spirits are alcoholic beverages. Navigation along a river or canal is freight transport, while the same canal's water considered as a delivered resource is here. Two figures give the scale: roughly seventy percent of the fresh water people use goes to agriculture, and the United Nations Environment Programme ranks water first among all the resources humanity consumes, ahead of sand and gravel.