I have a cold air humidifer. That is, it relies solely on the nature of water evaporation to humidify -- it doesn't emit a mist. In terms of humidifying, it works well. The problem is that, after two days or so of the water sitting in the open tank, it begins to smell. After 3 days it's not pleasant. I'm able to prevent the smell by changing water on a daily basis, but I don't think I should have to.
Currently I add a drop of dish soap to the water; this acts as a surfactant, letting the water evaporate more easily. I would have thought this would ****** the growth of odor-causing bacteria. Can anybody suggest an additive that would prevent growth of bacteria and is still safe to be in contact with? My guess is that the dish soap doesn't evaporate, so I probably don't come in contact anyway.