Product review (3 stars): Doesn't Last Long With Hard Water
Just to provide an illustration of the warning that "hard water usage may require more frequent replacement," I live in the Los Angeles area where our city water is fairly hard, and these cartridges only last about three weeks before the white dust returns (I faithfully follow the soaking instructions each time). The humidifier is used in our bedroom and only at night. So, don't expect these to last 2-3 months as advertised unless your water is on the soft side.