Water Supplies

People sometimes ask “What water supplies should I use for my orchids?

Like most orchid-related things, “it depends” – mostly on the plants. Some plants are tolerant of pretty much any water supply, while others are very sensitive to water quality, particularly pH and dissolved solids.

Unfortunately, folks often mistake the true meaning of water descriptions, so let’s look at them closer, adding some use criteria.

  • Pure water is defined (for our purposes) as having essentially no dissolved minerals. It can be obtained in a number of ways, each having its own pluses and minuses:
    • Deionized (DI) water has been passed through a bed of various organic resins that extract the dissolved mineral ions. If size properly, these can be “on-demand” systems (installed in-line with your plumbing), but tend to be expensive, as the resin beds need to be recharged or replaced periodically.
    • Reverse Osmosis (RO) achieves the same result, but does so by passing the water through a membrane having pores so small that they can only pass water molecules, blocking the flow of those dissolved ions. RO systems are relatively inexpensive (purchase price of a few hundred dollars at the most, plus low cost component replacement) in terms of price per gallon, but tend not to be on-demand types, as household units typically only deliver a few ounces per minute or pure water, necessitating some sort of storage tank for periodic uses of larger volumes of water.
    • Distilled water uses an energy source to cause the water to evaporate, leaving the solids behind, then cools and condenses that pure water for use. Unless you have a “solar still”, these are costly, and in any case will also require storage containers.
    • Collected Rainwater or Melted Snow are really nothing more than water that has been distilled by nature. As such it is free, but again, requires storage volume. Relying on nature to provide your water supply is not particularly reliable in many places.
    • Air Conditioner or Dehumidifier Condensate is again, a “distilled” source, but instead of waiting for nature to condense the moisture from the air, we use a refrigerant to chill the air and force the condensation. This is a limited-volume source that is best utilized in warm, humid climates, but still needs tanks to store it, as most units only produce a trickle.A note about collected rainwater or melted snow, or A/C condensate: where you live (industrial/urban/rural) can affect the quality of the water, due to air pollutants. You should also be aware that your roof, being a place for airborne “crud” to settle, can contaminate the water at the start of rainfall, and new shingles can release organic chemicals into that water, as well.
  • Purified water can vary greatly in its chemistry, but is most often simply passed through filters to remove sediment and dissolved organic compounds. No minerals are removed from the water. A Brita filter is in this category. This is an on-demand source, and doesn’t cost all thaT much, but is of limited value.
  • Softened water has been passed through a chamber in which sodium chloride dissolves in the water, forcing the ions of calcium, magnesium, and iron to precipitate, or settle out of solution. Do not use such softened water on your plants, as the sodium can be toxic to them.
  • Spring water is just that – water that has been drawn from the underground aquifer and bottled for distribution. While it is lovely for drinking, it usually contains plenty of dissolved minerals, making it taste great, but offering no advantage for orchid growing. The same is true of well water, as it’s the same stuff, just pumped locally, rather than bottled. If you’re purchasing it in bottles, the cost is too high to compete with most well- or tap waters.
  • Tap water will vary all over the map – literally. It can come from wells, rivers, rain and snow melt runoff, any number of sources. In some places – the southwestern part of the US, for example – the water is so mineral-laden and alkaline, that it is virtually unusable for watering, as-is. In New York City, on the other hand, the tap water is so mineral-free that growers should use fertilizers that provide essentially all of the needed nutrients, as the water brings essentially nothing with it. Fortunately, your municipality can often provide you with a water quality report, and while the actual chemistry may vary a bit during the year, it ought to give you a good idea as to what you’re getting. The costs of tap water vary quite a bit as well, but at least it’s usually readily available.

We like the idea of using pure water for all of our orchids for two reasons:

  1. In nature, pure water – rain or dew – is all the plants ever see.  It may pick up nutrients as it cascades through the forest canopy, but that’s typically 25 ppm of total dissolved solids (TDS) or less, and is only present when the rain first starts falling.  After that, it’s pretty pure.It stands to reason that the plant will have evolved to expect that, so hitting them with higher levels of dissolved solids, whether in the water itself or through the additions of fertilizers, might be more than they can handle.
  2. By starting with the chemical “blank slate” that pure water is, and adding a fertilizer designed specifically to provide the minerals in the correct proportions at the proper pH (the Greencare Orchid Special for RO), we know exactly what our plants are getting, so can manage their nutrition precisely, and adjust in a controlled manner as needed. Our plants have responded by growing larger, having more leaves, and blooming better than ever.

There is an additional benefit if you mist for humidification or cooling. Dissolved minerals in the water can leave a buildup on your plants’ leaves. Misting with pure water avoids that altogether, and you’ll see that your plants really take on a glossy, clean appearance.

Unless you live in New York City or where the water supply is primarily snow melt captured in reservoirs, and if you’re a serious hobbyist, you will probably find that adding an RO system to your existing water supply is the best way to go, as in the long run, the cost is a fraction of a penny per gallon.

Using Science & Logic to Improve Horticulture