Abstract: A mobile concrete mixing unit has an aggregate bin divided into two compartments by a water tank provided within the aggregate bin. A hydraulic reservoir is provided within the water tank in order to cool the hydraulic fluid within the hydraulic reservoir and warm the water within the water tank. The water tank also helps to keep the aggregate warm and flowable when used in low temperatures. A lower portion of the water tank includes sides that slope inwardly so that aggregate within the bin can drop freely onto a conveyor belt without bridging between the water tank and the sidewalls of the aggregate bin.