An aspersorium is an open holy vessel used to supply an aspergillum. One flask placed into it provides 3 charges, and it can hold up to 9 charges. Dipping an aspergillum consumes 1 charge.
While you carry an aspersorium containing any charges, each time you are attacked or required to make a Reflex Saving Throw, it loses 1 charge. A filled aspersorium is still wielded in one hand despite its increased EP.