An acequia (Spanish: [aˈθekja]) or séquia (Valencian: [ˈsekia]) is a community-operated waterway used in Spain and former Spanish colonies in the Americas for irrigation. Particularly in Spain, the Andes, northern Mexico, and the modern-day American Southwest, acequias are usually historically engineered canals that carry snow runoff or river water to distant fields.
The Spanish word acequia (and Valencian séquia) comes from Classical Arabic "as-sāqiya", which means "the water conduit". The Arabs brought the technology to Spain during their occupation of the Iberian peninsula. The technology was adopted by the Spanish and utilized throughout their conquered lands, except in e.g. Mendoza, Argentina where acequias today run along both sides of all city streets but originally were dug all around by the indigenous Huarpes long before the arrival of the Spanish.
Most acequias were established more than 200 years ago; many continue to provide a primary source of water for farming and ranching ventures in areas of the United States once occupied by Spain or Mexico.
Acequias are gravity chutes, similar in concept to flumes. Some acequias are conveyed through pipes or aqueducts, of modern fabrication or decades or centuries old (see transvasement). The majority, however, are simple open ditches with dirt banks. In many communities, the ditchbanks are important routes for non-motorized travel.
Known among water users simply as the Acequia, various legal entities embody the community associations, or acequia associations, that govern members' water usage, depending on local precedents and traditions. An acequia organization often must include commissioners and a majordomo who administers usage of water from a ditch, regulating which holders of water rights can release water to their fields on which days. In New Mexico, by state statute, acequias as registered bodies must have three commissioners and a majordomo. Irrigation and conservation districts typically have their own version of majordomos, usually referred to as "ditch riders" by members of the districts.