Many orchid growers look at water purification as a way to “step up their game” in providing for their plants. Unfortunately, unless you start with a few facts, many do things that don’t achieve what the want, or conversely, do things that they needn’t bother.
Yes, orchids do best when given very pure water, supplemented with a tiny amount of the right fertilizer, but that doesn’t mean that your water is bad. Here are some questions to be answered before moving forward.
What is in your water supply to start with? Is it too hard? Is it chlorinated? Is it softened?
“Hard” water typically contains excessive levels of calcium-, magnesium-, and/or iron carbonates. If you have buildup on faucets and cooking utensils, or excessive mineral buildup in your plants’ pots and potting media, it’s probably detrimental to some degree to your plants, as it can interfere with the uptake of other nutrients. If your plants have dull-, rather than shiny leaves, hard water may be the problem.
“Chlorinated” water is a rather broad term, as there are several ways that can be accomplished. If your provider injects chlorine gas, letting it stand open overnight will usually let it dissipate. If sodium hypochlorite, the active ingredient in household bleach, is added to the water, the chlorine will also be lost to the atmosphere, albeit much more slowly and we really don’t want the excess sodium. Chloramine is the “gold standard” nowadays as its persistence in the water keeps it safer for a long time, but that also means that letting it stand in an open container does nothing.
“Softened” water has used ion exchange resins to substitute sodium chloride (yes, table salt) for the “hardness minerals” in the water. Over time, it will kill your plants.
Once you have identified what you want to remove, you need to understand how to go about it.
If chlorine is the issue, carbon filtration is a great option. Activated carbon filters remove chlorine and organic molecules that may smell bad. My water here in NC is quite pure, but is chlorinated, so I simply use a carbon dechlorinator to purify it for drinking, cooking and for irrigating my plants. if you only have a few plants, something like a Brita filter also uses carbon, but that can get pricey in short order.
Carbon will not remove dissolved minerals, so if your water is hard or has been softened, it will not help at all. In those cases, we must go to different technologies.
The most common technique for removing dissolved minerals from the water is reverse osmosis. Your line water pressure pushes the water through a membrane that can reject almost all of the dissolved solids.
Such systems are not “on demand” water supplies, so require that you set up water storage and delivery means. If you only need small volumes of water, counter-top RO
systems are available that let you simply fill up a few milk jugs with pure water, then put the unit away again.
Another technique for removing dissolved minerals from water is deionization. These can be on-demand water supplies, as water travels through a chamber containing resins that trap the dissolved minerals as it passes through. The water exiting the cylinder is almost as pure as distilled water, but that level of purity really isn’t necessary for orchids. Plus, those resins have a finite capacity, so must be replaced periodically at significant expense. Zero-Water pitchers use DI resins to purify water, but again, at a significant cost-per-unit.