Sufficient agricultural water for irrigation is an important factor in food production, yet available fresh water only occupies 1% of the water on the earth. Seawater, through desalination, becomes rational solution to provide agricultural water due to abundant quantities and beneficial nutrients for crops. Hydroponic using desalinated seawater as medium is an approach to accomplish food security, especially in the arid and coastal areas. This study aimed to examine the growth of mustard (Brassica juncea L.) on a blend of fresh water and desalinated seawater using sulfuric acid activated zeolite as hydroponic medium. The experiment consisted of one control (100% fresh water+AB mix) and treatments namely a blend of 70% fresh water and 30% desalinated seawater using sulfuric acid activated zeolite with various sulfuric acid concentrations i.e 0.5, 1, 1.5, 2, 2.5, 3, and 3.5 N. The growth of mustard in blend of 70% fresh water and 30% desalinated seawater was lower than fresh water. A blend of 70% fresh water and 30% desalinated seawater using 1.5 N sulfuric acid activated zeolite showed no significant different mustard growth compared with fresh water medium and the fresh weight reduction was about 24%. Insignificant different growth between optimum treatment and control indicated a simple desalination method in this study can be utilized to desalinating seawater for hydroponic medium purpose. This finding emphasized that the simple seawater desalination method in this study for hydroponic medium was promising and interesting to be further developed for sustainable water management and agriculture.