The reservoir door might not be properly attached. If the door does not fit cleanly over the reservoir opening, first try to re-attach the door so that it fits cleanly over the reservoir opening. In the AirFloss handle you will see the opening leading to the reservoir has slots into which the door hinges snap. Simply snap the door hinges into the slots in the reservoir opening. If the reservoir door is broken or if it will not stay locked in the handle, a new door may be necessary. Contact the Philips Customer Call Center or visit the Philips Support website to contact a Philips representative.