Product review (1 stars): Lasts a mere three days!
I cleaned the unit (Graco 4-gallon cool mist) every day and filled it with water run through a very good quality countertop filter.  Even doing this, I went through two of these $11 filters per WEEK (TWENTY-FOUR TIMES as many filters as stated by the manufacturer!), and simply couldn't afford to spend nearly $90 a month (just in filters!) to run a humidifier.  That is, putting it simply, absolutely insane.  Design is faulty -- filtered water shouldn't trash a brand-new filter in less than four days.  I don't know anyone who could afford $90 a month for humidifier filters.