Most of the world's orchids are epiphytes (grow in trees) in nature, and they have evolved with relatively pure rain water as their source of moisture. Orchids are more sensitive to the quality of water than most other plants, and this sensitivity should be considered if your orchids do not grow well and bloom for no obvious reason.

In general, the tap water available in most developed countries is acceptable for orchid growth, especially if you follow the practice of potting with media with the correct moisture retention characteristics, use pots with many holes for good drainage, and water thoroughly to flush out minerals and fertilizer salts.

If you notice a buildup of white deposits on your clay pots, your area is known for high mineral content in the tap water, you see other signs of minerals (such as spots on glassware), you have a water softener system in your house, or your orchids don't thrive inexplicably, then you should have your water tested.

The tests may reveal that your tap water is over-treated with chlorine or other purifying chemicals, is too acidic or too alkaline, or contains too many minerals to be suitable for sensitive orchid roots. If you have a water softener system in your house, the tests will likely show that the level of sodium (Na) in your water is too high.

What Water Should be Used?

There are basically three types of water available at your home: pure water, hard water and softened water.

Pure water is the best type of water for your orchids. Reverse-osmosis, distillation, or de-ionization are some of the methods used to filter out the salts and minerals in the water. Collected rain is another source of relatively pure water.

Hard water or softened water is commonly present at your tap. The former contains a high amount of dissolved minerals, while the latter has high sodium content. You should never use softened water on orchids -- the sodium (Na) will dehydrate the roots and may eventually kill the orchids.

Hard water is generally less damaging to orchids, as orchid roots have a greater tolerance for minerals that don't include salts. Watering with hard water means that you should thoroughly drench your media to help dissolve the mineral deposits. However, the minerals will eventually build up in the media and may require watering with pure water to flush the minerals, or even a change of media.