Pyrolysis of pyrobituminous shale rock to extract products such as fuel oil and gas generate a liquid by-product called shale water (SW). In this study, the physical-chemical characterization of SW was performed and the effects on plant growth, mineral nutrition, and food safety were evaluated when applied via foliar in lettuce crop. Shale water showed a great diversity of organic compounds, minerals, and trace elements. The application of SW in lettuce resulted in no phytotoxic effect or accumulation of toxic elements to human health within the doses tested, and increased yield and the accumulation of several mineral nutrients in the leaves. The absorption and accumulation of zinc, copper, cobalt, molybdenum, and manganese was also improved when these minerals were applied together with SW. These results suggest that SW plays a role as a biostimulant and could be used in agriculture as a safety alternative to increase yield and biofortify crops.