functions, first as a normal bag to carry any personal belongings, second, you can install the water bag to use as a hydration bag.-PROFESSIONAL 3L HYDRATION BLADDER: The 3L liner inside detaches from the backpack for easy cleaning and assembly. The rubber mouthpiece has a simple switch valve to stop water flow when needed, ensuring a leak-free outdoor experience. Our water liners have passed pressure tolerated tests and have been put to the test to the highest quality standards.-The bag with a 100cm length water pipe can be easily placed in the bag for you to drink water with compressive resistance to abrasion.-Tube connected to the bottom of the bladder.-Can be put into a backpack and backpack's shoulder strap.-It can be used to store water at -20 to 50-degree celsius.-This backpack is very suitable for daily travel in the city, short walks, garden barbecue, party and so on, partition clear, in daily use can quickly find the required small objects, such as mobile phones, wallets, pens, notepads, IPAD, etc.-This product is a compact rectangular city backpack, with military characteristics of the shape. Suitable for jogging, running, cycling, etc.-Y-shaped compression band, to help shape the bag and the adjustment of the structure, riders can take the Helmet on the front of the bag with an elastic band fixed-Adjustable shoulder strap and waist belt, full-featured-Comfortable backfill and softly curved shoulder strap to reduce shoulder pressure when carrying