The increasing use of geothermal resources for generating electrical energy has brought the negative impact of geothermal fluids on the surrounding agricultural areas in Turkey. Alkali grass is one of the halophyte plant species that is spreading in marginal areas such as waterlogged, excessively alkaline and salty. We conducted the study to test the response of alkali grass genotypes to geothermal and mineral water used as irrigation water. Geothermal water negatively affected the observed traits by 14.01% (panicle length) and 64.21% (seed yield). The number of tillers per plant for biomass and the number of panicles per plant and plant height for seed yield were the determinant traits. Genotypes XII and XI were determined as seed-type, whereas genotypes IX and VIII were determined as biomass-type according to the Biplot graph.