Water bag can be placed in the bicycle backpack, wear - resistant anti - splash anti - tear fabric, with light wear characteristics. The warning protection products made of reflective materials can produce the effect of reflection under the irradiation of light source, which can give a certain warning to pedestrians or vehicles in the dark. Water bags can be placed in outdoor sports, and water bag catheters can be placed at the outlet of water, so as to facilitate cyclists to timely replenish water at any time and anywhere. The color check button can be adjusted according to the back of the appropriate tension, while fixing the shoulder strap does not slip, at the same time the buckle is an emergency rescue whistle. S type shoulder strap design, in line with ergonomics, effectively disperses shoulder pressure, honeycomb mesh hole has good air permeability and moisture absorption function, making back more relaxed. The elastic rope imitates the ecological structure of dragonflies. It can expand and contract the design of outboard.