A water bag of the present invention includes a soft bag with an intake, a lid detachably covering the intake of the bag, a hose having an end connected to the bag and a mouthpiece connected to a free end of the hose. The hose has a water inlet to inject water into the soft bag and a cap detachably covering the water inlet. Therefore, water may be injected through the water inlet directly without having to take the soft bag out of the backpack.