The filter in a humidifier acts as a cleaning agent to remove minerals and bacteria from the water before the water is dispensed into the environment. This can be an important part of the humidifier use, particularly if the humidifier is used frequently, if the water used in the humidifier is not pre-filtered, or if the humidifier's users have allergy or respiratory sensitivities.
It is important to note that a humidifier with a filter will not be significantly different than a non-filter humidifier if the filter is not changed on a regular basis. Humidifier filters, including wick filters, saturate quickly and require changing approximately every two months. If the unit has a permanent filter, the permanent filter should be cleaned every two to three weeks. Check the humidifier user manual for specific filter maintenance, cleaning and replacement instructions.
Humidifiers that do not utilize a filter often have a cartridge that is used to demineralize the water and/or an antibacterial stick to help remove bacterial and minerals from the water. While perhaps not as thorough at filtering debris, particles and bacteria from the water, these humidifiers may be less expensive than traditional filter humidifiers and may take less time to maintain.
Regardless of whether a humidifier has a filter or not, all humidifiers require regular cleaning and maintenance to help keep the unit clean, the water fresh and the dispensed steam or mist largely free of bacteria, germs or mineral content. Wipe down humidifiers with vinegar or bleach on a regular basis and clean the water tank and scrub it with vinegar or bleach as well.