The only thing that you need is distilled water, that you can buy at any local grocery or drug store. Never use tap water as it has minerals and it will cause mold to grow in the humidor and on the cigars. Some prefer Humidor activation and maintenance solution. This solution will allow the distilled water to evaporate at exactly 70% Relative humidity and it will allow for uniform humidity inside the humidor. This is only used when you set-up the humidor and every 3 months or so thereafter. It still requires that you fill the humidifier with distilled water every 3 to 4 weeks or so.