Things You'll Need
In an evaporative humidifier, the wick (or filter) absorbs water from the water reservoir in the machine. The purpose is to provide a large surface area for the water to evaporate and humidify the room. In order to maintain the benefits of having a humidifier in the room -- which includes creating cleaner, breathable, dust-free air -- you need to make sure that this wick does not dry out.
Refill your humidifier before the reservoir is empty. In order to prevent your wick from drying out, it needs to have consistent access to a water supply. Look at the reservoir water tank on your humidifier, and find the line that represents the low-water line. Never let the water go below that line.
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Clean your wick once a week, or if you find that the wick is frequently getting dried out. Regular cleaning will help the wick maintain its moisture. Soak the wick in vinegar for 20 minutes. A vinegar soak will help remove hard-water deposits on the wick that may be causing it to dry out. When you have finished soaking it, briefly run it under cold water, and put it back into your humidifier.
Change your filter wick every four to six weeks, especially if you use your humidifier every night. The exact time that you should allow to pass before changing your filter does depend slightly on the type of humidifier that you own and the conditions in your room, but generally you should not go longer than six weeks without changing the wick. Consult the manufacturer's instructions for your particular machine to learn the exact time when you should change the wick, and remember to purchase a replacement wick that is specifically designed to work with your machine.