Water is the foundation of hydration, but OTE marathon drinks do much more than simply resupply fluid lost through sweating. They also contain carbohydrates and electrolytes, both of which are spent during exercise and are key to fuelling optimal performance.
Carbohydrates are the energy source that powers the body, so replenishing them ensures you can run harder for longer. Electrolytes are lost through sweat, and resupplying these efficiently allows muscles and nerves to continue operating at a high level.