In a water bottle of the type for inverted insertion to a water cooler, the water bottle having a bottle body, a bottle neck terminating in a bottle opening, a cap assembly overlying and sealing the opening, an improvement to the cap assembly is disclosed. The cap body attaches the cap body to the water bottle at the neck overlying the opening. Two portions of the cap are present. A first cap portion includes a membrane attached to the cap body and sealing the bottle opening. A second cap portion has an exposed exterior top overlying the bottle opening and includes an interior surface exposed to the bottle opening. This second cap portion at the interior surface exposed to the bottle opening is moveable to a first short interval towards the membrane and to a second long interval away from the first cap portion at the membrane. A membrane piercing member having a mounting portion attached to the second cap portion at the interior surface and a membrane piercing portion extending away from the second cap portion towards the membrane. The membrane piercing portion having a length less than the second interval but greater than the first interval. A water passage is defined on the second cap portion for permitting water to flow from the membrane ruptured by the membrane piercing member through the second cap portion.