A water reservoir includes a reservoir base configured to hold a predetermined maximum volume of water to be used for humidification of pressurized breathable air, a reservoir lid pivotally connected to the reservoir base to allow the water reservoir to be movable between an open position and a closed position, the reservoir lid comprising an inlet and an outlet, and a seal configured to sealingly engage the reservoir lid and the reservoir base when the water reservoir is in the closed position, wherein the reservoir base includes an overfill protection element having an egress path for water at a predetermined location.