Abstract Reuse of drainage waters is an attractive management option that has been proposed for many irrigated agricultural areas. In California's San Joaquin Valley (SJV), however, drainage effluents are not only saline, but may also contain potentially toxic trace elements such as selenium and molybdenum. Crop suitability for reuse systems depends on the influence the sodium sulfate-dominated waters have on biomass production, plant sustainability, and mineral elements that are critically important for forage quality. Ten promising forage crops were grown in greenhouse sand cultures irrigated with synthetic drainage waters dominated by Na 2SO 4 with an EC of either 15 or 25 dS/m each containing 500 μg/L Se and Mo as SeO 4 2− and MoO 4 2−. Plant material was analyzed three times for mineral content and selected trace elements that may have a profound influence on ruminant health. Trace element concentrations indicate Se toxicity is of little concern, but that high concentrations of both Mo and S in the herbage may lead to Cu deficiency in ruminants. Similarly, high K/Mg and K/(Ca + Mg) ratios in many of the legume and grass forages, respectively, indicate that there may be potential for development of sub-normal Mg levels (hypomagnesaemia) in ruminants. However, each of these disorders can be avoided or corrected with dietary supplements. The most concern regarding ruminant nutrition based on these data is sulfur toxicity. Sodium-sulfate dominated drainage waters will likely elevate forage S concentrations to levels that might cause excessive sulfide concentrations in the rumen and potentially lead to serious neurological disorders affecting animal health.