Viticulture in Baja California (Mexico), located in a semi-arid region, is limited by the availability of water. Treated wastewater (TWW), however, could be used to irrigate some crops. Therefore, the objective of this study was to assess the effect of irrigating grapevines with TWW on the microbiological and chemical quality of grapes in the Guadalupe Valley. Five-year-old Tempranillo grapevines were irrigated with 10 or 20 L week(-1) of TWW from the El Sauzal wastewater treatment plant; for the control treatment, water from the Guadalupe Valley aquifer was used. The analysis showed that TWW satisfied all the parameters of the norms NOM-001-SEMARNAT-1996 and NOM-003-SEMARNAT-1997 for restricted and nonrestricted irrigation, as well as for direct and indirect contact during the study. No significant differences (p > 0.05) were observed in pH, titratable acidity, the concentration of soluble solids (sugar) or yeast assimilable nitrogen in the grapes, regardless of the type of water used for irrigation. The concentrations of the Ca, Mg, Na and K ions were not affected by the irrigation treatments (p > 0.05). This study shows that TWW from the El Sauzal treatment plant did not cause short-term negative impacts on the quality of grapes for vinification, and that treated water could be used to irrigate this crop.