The moisture collected by a dehumidifier is condensed atmospheric water, essentially recycled rainwater that offers a free source of water for your plants. Repurposing this water is a sustainable practice that conserves tap water. While chemically similar to distilled water, it is not pure and comes with important caveats regarding cleanliness and nutrient content. Using it safely requires understanding its composition and the potential risks collected from the machine.
Understanding Dehumidifier Water Composition
The process by which a dehumidifier collects water is comparable to distillation, leaving behind dissolved solids. The resulting condensate has a very low concentration of Total Dissolved Solids (TDS), often measured at less than 20 parts per million (ppm). This makes it significantly softer than typical tap water, which can range from 60 to over 600 ppm.
Because the water is collected through condensation, it lacks minerals like calcium and magnesium necessary for plant health. This mineral-free nature is beneficial, as hard water minerals can accumulate as salt deposits in the soil, damaging plant roots. The \(\text{pH}\) of dehumidifier water is typically neutral (around 7) or sometimes slightly acidic, a characteristic shared with rainwater.
Identifying Potential Contaminants and Risks
The primary safety concerns stem not from the condensation itself, but from the appliance’s internal environment. The warm, dark, and stagnant conditions within the collection bucket create an ideal breeding ground for microbial growth. This can introduce mold, mildew, and bacteria, such as Legionella or Pseudomonas, to the plant’s soil or roots.
A second risk is the leaching of heavy metals from internal components, such as the cooling coils. While modern units often show only trace amounts, older or poorly maintained machines may contain copper, lead, or aluminum. These heavy metals are toxic to plants because they inhibit root elongation and interfere with water uptake. The presence of chemicals or volatile organic compounds (VOCs) absorbed from the air also makes the water unsuitable for edible plants like herbs or vegetables.
Guidelines for Safe Plant Watering
To safely use this reclaimed water, routine cleaning of the dehumidifier unit is necessary to mitigate microbial contamination. The collection tank should be cleaned regularly with a mild bleach or vinegar solution to prevent the buildup of slime, mold, and bacteria. The collected water must be used immediately after collection and never stored for extended periods, as contaminants multiply rapidly.
Since dehumidifier water is nutrient-poor, it should not be the sole source of hydration for most common houseplants. It is recommended to supplement the water with a liquid fertilizer to ensure plants receive essential macronutrients and micronutrients. Alternatively, dilute the dehumidifier water with regular tap water (perhaps 50/50) to introduce some minerals while retaining the benefit of low \(\text{TDS}\).
The low \(\text{TDS}\) is particularly beneficial for plant varieties sensitive to mineral salts and chlorine, as it prevents the buildup of white mineral crusts on the soil surface. These sensitive varieties include:
- Carnivorous plants
- Orchids
- Ferns
- Spider plants
Avoid using this water on any plants intended for human consumption, such as home-grown produce, due to the potential for heavy metal or microbial contaminants.