Hydration matters because creatine can increase intracellular water in muscle, but there is no single universal liters-per-day target. Climate, sweating, training volume, body size, and kidney/heart status determine needs. A practical approach is aiming for pale-yellow urine, planning fluids around workouts, balancing losses from alcohol/caffeine, and considering electrolytes in hot conditions. In kidney disease or heart failure, fluid targets are individualized and “just drink more water” may be harmful. For higher-risk users, clinician/dietitian guidance is best.