This study aimed to compare the effectiveness of coach encouragement and hydration education in maintaining hydration status in youth judo athletes, addressing the lack of comparative evidence on hydration strategies. Forty-seven athletes (16 males, 31 females) participated in a four-day training camp. Hydration status was assessed before and after training under three conditions: no intervention (control), coach-guided fluid intake encouragement, and a brief one-time pre-training hydration education. Athletes were unaware of the intervention applied each day, and the educational session was presented without highlighting its experimental nature. Hydration status was objectively measured using urine specific gravity (USG) and urine color (UC). At baseline, 85.1% of athletes were hypohydrated based on USG. Both coach encouragement (p = 0.18) and hydration education (p = 0.22) were associated with the maintenance of hydration status, while the control condition showed a significant deterioration post-training (p = 0.02). Although no significant pre-post differences were observed in UC, both interventions limited the decline seen in the control group. Structured hydration strategies beyond thirst perception are needed for young athletes. These findings suggest that real-time fluid encouragement and brief educational interventions may help support healthier fluid balance during training.