Reglamento general de las medidas de las aguas (Mexico, 1761)
The printed rulebook that turned irrigation water in New Spain into a measured, divisible quantity. It defines the buey de agua as an opening one vara square and subdivides it into surcos, naranjas, reales and pajas, so that a grant, a sale or a lawsuit could name an exact share; it states the Roman and Castilian law behind the royal claim to water; and it was still the working standard when a Mexico City publisher reprinted it eighty-eight years later, with corrections.
Why this wins its question: Colonial Spanish American water units appear in English mostly as a glossary gloss - "buey de agua, a large measure of water" - with no geometry and no law behind them. This object gives the system as its own rulebook defines it: the buey as a one-vara-square opening, 2304 square dedos, decomposed into 48 surcos, 144 naranjas, 1152 reales and 20736 pajas, with the five-paja municipal toma of Mexico City; the legal premise that water is a regalia requiring a royal grant, and the limit of that premise in the common right to draw for domestic use; the citation of Avendano and Solorzano as the doctrine for the Indies and of the cedula of 15 October 1754 as the current instruction; the trade vocabulary and the aquiliges or hydromensores who gave sworn evidence in water suits; and the interdict De aqua pluviale arcenda as the remedy against a neighbour's works. It then prints the defect: measuring area alone let a steeper channel take more than its share, a flaw its 1849 editor corrects with a fall in front of each opening.
Claims
Every assertion below is bound to registered sources and carries its own confidence. Weight them; do not treat the page as uniformly authoritative.
The base unit is defined by an opening, not by a flow. A buey de agua is an aperture or data of square figure each of whose sides is one vara, so its area is one square vara; since a vara consists of 48 dedos or 36 pulgadas, that area is also 2304 square dedos or 1296 square pulgadas. Water was quantified by the cross-section of the hole it ran through.
The subdivisions are exact and they nest. A surco is a rectangle 8 dedos long by 6 wide, area 48 square dedos; a naranja is 8 dedos by 2, area 16 square dedos; a real de agua is 2 dedos by 1, area 2 square dedos; a paja is a square each of whose sides is a third of a dedo, area one ninth of a square dedo. Hence a buey is 48 surcos, or 144 naranjas, or 1152 reales, or 20736 pajas - a decomposition fine enough to divide a spring among a whole valley.
The system was municipal as well as agrarian, and the city's household unit was small. Two tables follow the definitions, the first for the rectilinear datas used to distribute irrigation water and the second for the circular openings that commonly supply public and private fountains, with their diameters and the sides of the squares circumscribed about them; and for the fountains of Mexico City the municipal measure or toma is five pajas.
The Reglamento's legal premise is that water is a royal regalia, which is what made a licence necessary before an aqueduct could be dug. It reasons that waters, lands and mines belong to the royal patrimony and are therefore called realengas, so that to possess them a private holder must allege and prove a special grant from the king; that only the prince has the right to distribute waters, and quasi-possessions in which the regalia is discovered are null; and that consequently nobody may lead public waters to their own land for irrigation without the prince's permission.
It also states the limit of that claim, in the one place where the private person wins. All the waters of public rivers are of public and common use as to personal and domestic use, so that anyone may draw what they wish for the relief of their domestic necessities - the general liberty is preserved even though conduction for irrigation is not. The authority given for this is Avendano's Thesaurus Indicus, cited by title, chapter and page, and the Institutes.
For the Indies specifically the Reglamento rests on the viceregal faculty and on a cedula it treats as the current instruction. It states that the king has granted the viceroys and presidents of the audiencia of New Spain ample faculty to make grants of lands and waters as goods belonging to the royal crown, that there is a particular privative tribunal for the matter, and that this is evidenced by the most recent cedula issued at San Lorenzo el Real on 15 October 1754, to which it refers the reader for everything touching the branch of lands and waters. The doctrine for the Indies is taken from Solorzano and Avendano rather than argued afresh.
The text is written for expert witnesses, and says so. Its author states that he explains the principal terms and decisions because they are needed for the discharge of the obligation of his fellow professionals in the sworn declarations required at the request of litigating parties for the exact justification of their claims, and because, as the maestro Saenz de Escobar and other authors hold, grave litigation commonly arises from the diverse senses of the names. It fixes the vocabulary - agugero, toma, data, puerta, merced, marco - notes that the practitioners of the trade are called aquiliges or hydromensores, and that the science of conducting and measuring water is called hydrometry.
It carries a remedy for the harm one landowner's works do to a neighbour, taken straight from Roman law. The interdict most to the purpose is De aqua pluviale arcenda, by which a civil action lies against those, expert or private, who build a dam or channel whose effect is that rainwater damages neighbouring third parties; if what a man does on his own land makes the water from the sky damage his neighbour's, the action lies against him, he must pay the damage caused and is obliged to destroy the work he made.
The measure had a defect that a nineteenth-century engineer states plainly, and this is the counterpoint the object turns on. Because area alone was measured, users who drew from different points and led the water down steeper channels obtained greater velocities and so enjoyed more water in proportion than others; Galvan's remedy, printed alongside the reprint, is to build a fall in front of each opening so that all the water enters its channel with the same velocity, and to prefer rectangular openings to circular ones, because the interested parties cannot themselves work out the quantity passing through the segments of a circle with the ease a rectangle allows.
The distribution rule the whole apparatus serves is proportional and is stated as such: the operation has for its object the just and equitable division of a quantity of water passing through an aqueduct between two or more interested parties, in proportion to the quantities granted to each by merced, purchase, lease or denuncio. Shares were of the flow rather than of turns of time, in the case the Reglamento treats first.
Its authority was a printing licence, and its life was long. The 1849 editor records that the Reglamento was circulated under the licence of the viceroy the marques de Cruillas, by decree of 16 April 1761 given on the parecer of Felipe de Zuniga y Ontiveros; that it has served as the guide in water business as the only thing printed in this branch, its circulation being taken as equivalent to approval by competent authority; and that it had been used for eighty-eight years without legal innovation in its juridical part, which is why he inserts it - while adding that hydraulics had advanced much in those eighty-eight years and that he will give operations of hydrometry yielding results nearer the truth than the methods the Reglamento proposes.
What this object rests on and what it does not. The Reglamento is read in Galvan Rivera's Ordenanzas de tierras y aguas, Mexico 1849, not in the 1761 printing, so the tier is secondary and the reprint's own editorial matter is distinguished in the claims from the reprinted text. The pages opened do not name the author of the 1761 Reglamento, only the viceroy who licensed it and the examiner who reported on it. And a rulebook is not a distribution: the measures show how shares were defined and litigated, not who held them, and the requirement of a royal grant to lead water meant that the party with the title, not the party with the field, held the flow.