Originally Posted by T.G

Can you get De-Ionized water? It's similar in purity.

In a pinch, you can use reverse osmosis purified water, but the problem is that the purity of RO water can vary greatly by the equipment used to produce it. Some of the larger, higher pressure systems are very close to distilled in purity, but some of the lower pressure or poorly maintained rigs can leave quite a bit of impurities in the water. Another thing to watch for is bottled RO water that states "Minerals added for taste", while I doubt that these minerals will affect your cigars in anything but an extremely long exposure (many, many years), they might plate out on your humidifier.