Water quality is an important factor in the successful cultivation of orchids. The choice of water source is critical, as the wrong kind can undermine the plant’s health over time. Understanding the specific nature of an orchid’s root system and its historical environment helps in making an informed choice about the best water to use.
Understanding Orchid Water Requirements
Most popular household orchids, such as Phalaenopsis (Moth Orchids), are epiphytes, meaning they grow attached to trees rather than in soil. In their native habitats, they receive moisture and nutrients from rainwater, mist, and highly diluted runoff. This natural water source is extremely pure, containing very few dissolved minerals or salts.
This evolutionary history resulted in a root structure, called velamen, that is highly sensitive to water purity. High levels of dissolved solids (minerals and salts) can damage this tissue and interfere with the plant’s ability to absorb moisture and nutrients.
The concentration of these substances is measured as Total Dissolved Solids (TDS), expressed in parts per million (ppm). Orchids thrive when the water’s TDS level is below 175 ppm, and ideally below 100 ppm, to prevent long-term root damage and salt accumulation. High TDS creates an osmotic imbalance, drawing water out of the roots instead of allowing the plant to absorb it.
Characteristics of Distilled Water and Its Suitability
Distilled water is produced by boiling water into steam and condensing the vapor back into a liquid. This process leaves behind virtually all impurities, minerals, and contaminants, resulting in water with a near-zero TDS level, often less than 1 ppm.
This extreme purity aligns with the orchid’s biological need for water that mimics its natural, dilute sources, making distilled water an excellent choice for irrigation. Low mineral content eliminates the risk of mineral buildup in the potting medium and on the roots. It also removes concerns about chemicals commonly found in tap water, such as chlorine and fluoride, which are detrimental to sensitive orchid roots.
The main consideration when using distilled water is that its purity means it contains no naturally occurring minerals, such as calcium and magnesium, required for growth. Growers must compensate for this lack of mineral content by using a complete fertilizer formulated to supply all necessary micronutrients. This is easily managed and allows the grower complete control over the plant’s nutrient intake.
Evaluating Alternative Water Sources
While distilled water offers the highest purity, several alternatives provide varying degrees of suitability for orchids. Tap water is the most convenient source, but its quality depends heavily on the local municipal supply. Hard tap water often exceeds 200 ppm TDS and contains high concentrations of mineral salts, such as calcium and magnesium, which lead to damaging buildup.
Tap water frequently contains added chemicals, such as chlorine and chloramine, which can negatively affect orchid health. Letting tap water stand overnight allows chlorine to dissipate, but it does not remove dissolved salts or chloramine. If tap water is the only option, test its TDS with a meter; if the reading is consistently above 200 ppm, an alternative is recommended.
Rainwater is naturally low in TDS and slightly acidic, making it an ideal choice that replicates the orchid’s native environment. Collecting rainwater may not be practical for all growers, and in areas with heavy air pollution, it can contain atmospheric contaminants.
Reverse Osmosis (RO) water is often considered the gold standard, as it uses a semi-permeable membrane to remove up to 98% of dissolved solids. RO water is almost as pure as distilled water, registering a very low TDS, and is a practical solution for growers with a larger collection. Like distilled water, it requires the addition of a complete fertilizer to ensure the plant receives adequate nutrition.
Signs of Mineral Buildup and Flushing Techniques
Mineral and salt buildup, often resulting from high-TDS water or fertilizer residue, presents several visible signs that indicate the orchid is under stress. A common sign is a white or brownish crusty residue on the potting medium surface, the pot rim, or exposed roots. Internally, high salt concentration can lead to fertilizer burn, appearing as brown or blackened tips on newly emerging roots.
This accumulation of salts interferes with the orchid’s ability to absorb water and nutrients, leading to stunted growth. To correct this, a process known as “flushing” or “leaching” is required to wash away accumulated salts from the potting medium.
Flushing involves drenching the pot with a generous volume of low-TDS water (distilled or RO water) until the water runs freely from the drainage holes. Run an amount of pure water that is at least twice the volume of the pot through the medium. Allowing the pot to soak for a few minutes before the final flush helps dissolve the salts. This corrective action should be performed at least once a month, especially if a high-TDS water source is used.