The best type of water for use in a humidifier for eczema is distilled or demineralized water. This is because this kind of water has reduced mineral content than regular tap water. Minerals can cause damage over time to the internal workings of the humidifier and can also release a kind of mineral dust into the air, which isn't good for your lungs or skin either. So, in order to get the best results from your humidifier, be sure to fill it up with distilled or demineralized water every time.