Salt production has been proffered recently as an alternative explanation to irrigation agriculture for the existence of canals and terraces at the Hierve el Agua site in Oaxaca, Mexico. This argument is based in part on new interpretations of the functions of two types of water-control features. Hewitt et al. (1987) consider the so-called "pocitos" to be natural, and the "registros" to be water tanks or collecting basins. Evidence that contradicts these interpretations is presented here. Pocitos, it is argued, were constructed intentionally in order to facilitate manual irrigation, and registros are drop structures built to regulate the flow of water after the arrival of the Spaniards. Salt making might have been carried out to some extent at the site, but only in late prehistoric and historic times. Hierve el Agua was principally an agricultural site throughout most of its occupation.