The Avalon Replaceable Filter is suitable for the model A2HUMIDIFIERWHITE and A3HUMIDIFIERWHITE. The filter is easily screwed onto the tank screw cap. Simply unscrew the old filter and replace it with a new replaceable one. The ion exchange filter will filter out unwanted minerals and bacteria in the water. It also reduces the limes in the water. By replacing the filter every 6 months, the lifetime of the humidifier will be extended.