Product review (5 stars): Take care of the filter and it will last a long time.
Some people just don't know how to use this product!!!!! I have 2 Vics 3900 humidifiers that I use to help keep the humidity in my home at 50%. First use filtered water (from the fridge that has a filter and water dispenser). Then put a 1oz. solid silver coin in the reservoir (a US silver Eagle or Canadian Maple Leaf coin) You can get one at any coin dealer. The silver won't let any mold, mildew, or any bacteria grow in the water. (you can check any hospital as they use silvered water in their operating rooms for just this purpose). Then every time you refill the reservoir put the filter back in upside down to even out the mineral deposits. Every now and then rinse the filter gently in warm water to reduce the buildup of minerals. I have used my humidifiers 24hours a day for all winter and with care the filter lasts 4 months or so.