2 liters heavy duty water reservoir for the Advance Hydration System (AHS). This design restrains the water reservoir snugly within the vest providing the utmost comfort and aids in cooling down the body during long operations. A strap inside the vest supports the water reservoir. This arrangement allows the water reservoir to stay in the up right position even when the reservoir is filled. This exclusive design prevents the reservoir from sinking to the bottom of the vest. This AHS vest places the reservoir directly against the back of the users. The AHS reservoir can be filled with cool or warm water.