Chemical quality of the Aconcagua river waters was cletermined, during the 1981/82 and 1982/83 irrigation seasons, to define their aptitude for irrigation. This study was based on pH, conductivity, soluble cationand soluble anion contents, SAR and Na%.
It was found that the waters had a low natural chemical charge, giving a river with good aptitude for irrigation at its entry to the valley. This charge increased progressively along the valley, as a result of several untreated wastewater discharges. Nevertheless, the use for irrigation of even those waters with maximum charge, like those from the lower sector of the river, showed low risk for plants and soils.
There were significant differences in absolute amounts and in rate of longitudinal changes of the chemical charge, between the two seasons studied. Both were maximum atthe 1981/82 irrigation period, and mininum at the next period; this was related with the amount of water flowing in the Aconcagua river each season.