Portable water storage system designed for easy access to hydration during physical activities. It typically consists of a lightweight backpack or vest with a built-in water reservoir, often called a bladder, and a hose for drinking hands-free. Hydration packs are commonly used for hiking, running, biking, and outdoor sports, offering a convenient way to stay hydrated without needing to carry bulky bottles. Some packs also feature compartments for storing small gear, like keys or snacks.