Increasing water demand and the use of treated gray water as an alternate source for irrigation are gaining global importance. This study evaluated the treatment of gray water using a natural adsorbent corn cob filter and investigated the effects of treated gray water on the growth of two spinach varieties (Sindhi and Prikli). The current study showed a significant reduction in morpho-physiological and antioxidant attributes in both spinach varieties when subjected to untreated gray water. However, treated gray water significantly improved the plant root/shoot ratio, water and chlorophyll contents, activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), plant soluble sugar contents, and reduced concentration of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) contents. Moreover, both spinach varieties significantly varied in response to gray water treatment. The Sindhi variety showed comparatively better growth and physio-biochemical attributes than the spinach variety Prikli. It can be concluded that treated gray water may be considered as an alternative for irrigation of horticultural crops.