One of the attractions of historical archaeology is the possibility to combine textual data with the archaeological record. In the world of Near Eastern archaeology, however, often the evidence of texts is taken to be the more reliable source, and elaborate historical reconstructions are occasionally made with little or no archaeological input. Such an imbalanced scenario is particularly dangerous with regard to ancient water systems, but the most successful attempts for Mesopotamia have been multidisciplinary collaborations, often incorporating ethnographic or ethnohistoric data.
Despite the perceived limitations of archaeological data, the most successful irrigation studies have involved them, for several reasons. The written sources on irrigation derive mostly from royal inscriptions. These texts reflect the priorities of the royal households that commissioned them, priorities that emphasize the legitimization of existing power structures. They describe not an objective reality (if such a thing is ever possible), but rather an idealized situation that supports the political agendas of the text-producing elite. Rarely do the political interests of the text producers correspond to the academic interests of modern scholars. For instance, royal inscriptions will emphasize the agency of the king in creating water systems (often acting with the blessing of the gods), but will fail to mention the preexisting systems that the king expanded, or the local systems of water sharing that brought water to individual fields.
Very often, the empirical elements of water systems were not considered significant enough to be mentioned. Yet for archaeologists, the physical dimensions of those systems are important for conclusions about economy and society. Elements of system scale (e.g., width and depth of canals, length of system, volume of water, irrigated area) are rarely described. Yet these elements are critical for assessing the extent of political authority, whether through control of land, or through the ability to mobilize the labor necessary for system construction. The absolute scale of an irrigation system could help archaeologists determine whether it was a critical element of the subsistence economy or a vanity project. When done on a regional scale, archaeological evidence can overturn major theories of social evolution; for example, the once-influential hydraulic hypothesis of Karl Wittfogel (1957) is largely out of favor, since Robert McCormick Adams demonstrated that urban settlement patterns preceded major irrigation systems by a millennium.