One aspect of the invention is an apparatus including an alarm for alerting an operator to recharge a humidifier, wherein such alarm is generated other than through the use of a humidity sensor. In one embodiment the total work performed during heating and hydrating an insufflation gas is measured and an alarm generated when the total work performed exceeds a particular threshold. In another embodiment, a flow meter is used to measure the total flow of insufflation gas so that when the total flow of insufflation gas reaches a predetermined level an alarm is activated.