Humidifiers can be a breeding ground for bacteria and fungus if not cleaned regularly, and the filter is no exception. The humidifier filter must be replaced regularly, but hand-cleaning can extend its lifetime and improve air quality. This method will work with most humidifier filters, but keep in mind that paper filters cannot be cleaned. Heavily soiled filters, and those that show signs of mold growth, should be replaced rather than cleaned.
Remove the humidifier filter from the machine and brush or vacuum lightly to remove any loose scale, dirt or dust. If the filter is wet from recent use, skip this step.
Combine one gallon of water and one cup of undiluted white vinegar in a plastic pail or bucket.
Completely submerge the humidifier filter in the vinegar and water solution and allow to soak for 20 minutes to loosen scale and buildup. You can swish the filter around in the water every few minutes to speed up the process.
Remove the humidifier filter from the solution and rinse several times under running water. If your humidifier uses a soft filter, you can squeeze out excess water gently between rinsing. Don't squeeze rigid filters. Never wring or twist the filter, as this may damage it.
Allow to dry completely at room temperature before replacing the filter in the machine. Don't try to hasten the drying process by using a source of heat; this may damage the filter and render it unusable.