Cost aside, is there any benefit to occasionally adding natural mineral water when watering houseplants or outdoor container plants? I recall that gardeners in Europe do so because it mimics rainwater. I have also heard pros and cons on using distilled water, such as from a dehumidifier, for potted plants.

The best type of water for houseplants is rainwater or melted snow. Distilled water can be used but you may be deterred by the cost and work carrying the jugs into the house. Tap water (well or city) is generally suited for most plants. The water should stand overnight in a container to allow it to lose some of the chlorine. Also, it is best if the water is at room temperature. Both hard and soft water can be harmful to your plants as they can contribute to a build-up of excessive salts in the soil. Hard water contains salts of calcium, magnesium and iron. Plants use these salts in very small quantities but, in large amounts, they become toxic. Softened water is even less favorable because the softening process exchanges calcium salts that have no use. In short, save your money and collect that rain or snow – it’s free.