Not familiar with the model, but some of them have a tank or a tray for the water to wick from. If it is a mist style or drip from the top, then you probably only need to worry about the filter.
You could take the filter out occasionally and soak it in something like this http://www.amazon.com/Holmes-S1705-Humidifier-Water-Treatment/dp/B0002TSA8S/ref=zg_bs_3737531_6. Just watch for the lime scale buildup on it.