In this study, the geothermal water (GW) was replaced with 25% (GW25), 50% (GW50), 75% (GW75) and 100% (GW100) of the volume of the Schlösser culture medium (SM). The biomass concentration was determined to the higher in the GW50 (1.324 g/L) than in other groups (GW25, GW75, GW100 and SM). The highest protein content and phycocyanin purity ratio were found in the GW75 medium containing 116.6 times higher phosphate than the SM. The chlorophyll, phycocyanin, protein, dry biomass, mineral and amino acid in groups prepared by mixing Schlösser medium and geothermal water mix (GW25, GW50 and GW75) were better than geothermal water (GW100) and the SM. It is concluded that using partial geothermal water in Spirulina production is efficient considering the parameters, i.e., biomass yield, protein, mineral and chlorophyll contents, and also return of investment.