Large opening for easy cleaning: CHERAINTI 2l hydration bladder has one of large opening; and the big opening makes for easy pouring of water; It is also fairly wide for a hand or bottle brush easily access to the interior water bladder for hiking backpack; The screw on cap goes on and off easily; for cold water, simply add ice cubes directly from a scoop or refrigerator ice dispenser；the smooth inner of water reservoir promotes health and is easy to clean