Distilled water is supposed to be the best. That gets pricey too if you buy it by the bottle. Some bottled water I hear is not the best for your plants as it still certain minerals or deposits that take the nutrients out of your plants. (but it is better than straight unfiltered tapwater) If you fill a jug with tapwater and let it sit for a few days the clornine will evaporate giving you that "distilled" characteristic.