If your tap water is very hard or contains limescale and you're a big plant care professional, you may have already considered whether distilled water is a good choice for your green companions. But is it really better, and does it give your plants what they need?
Should you water houseplants with distilled water?
Distilled water can be beneficial for some plants, especially if the tap water is very hard. Plants sensitive to limescale, such as orchids or carnivores, particularly benefit from soft water. Distilled water is also a good choice for spraying leaves to prevent limescale stains.
However, pure distilled water should never be used for watering on a regular basis, as it contains no nutrients and can cause osmotic problems. A mixture of sterile water and tap water or rainwater is a better alternative.
Are there plants for which distilled water is particularly suitable?
Plants require minerals and trace elements to grow, which aren't found in sterile water. However, there are some plants that are particularly sensitive to limescale, water hardness, and minerals in the water and therefore require very soft water. These include:
Which plants like calcareous soil?
Not all plants like soft water. Some plants prefer calcareous water for watering because it's in keeping with their natural habitat. They can be safely watered with tap water, even if it's hard:
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lavender
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olive tree
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rosemary
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Succulents
Is distilled water good for plants in mineral substrates?
If plants are kept in mineral substrates such as pumice, lava, or zeolite, distilled water can be beneficial. Hard water can lead to salt and lime deposits over time, which can be problematic for sensitive plants. Distilled water prevents these deposits. However, it's important to fertilize selectively. Nutrients aren't stored in these substrates but are added with the watering.
Organic fertilizer mixed with distilled water – effects on nutrients
Organic fertilizers provide nutrients that are processed by microorganisms in the soil. These require a stable environment to function optimally.
Because distilled water lacks minerals such as calcium and magnesium, it lacks a buffering effect. This can cause soil pH to change more quickly, which can impair nutrient availability and cause deficiencies.
Therefore, it is better to mix distilled water with tap or rainwater to stabilize the pH and promote nutrient absorption.
The best water to spray against limescale stains
Using sterile water has the advantage that it doesn't leave unsightly leaf stains when spraying plants. Large-leafed plants like Monstera or Strelitzia particularly benefit from this. Therefore, if you regularly spray your plants, you should opt for distilled or rainwater in the long run.
Why can distilled water be bad water for irrigation?
Distilled water contains no essential minerals or salts. When plant cells come into contact with distilled water, an osmotic imbalance occurs.
What does osmosis mean?
Osmosis is a physical process in which water flows through a semipermeable membrane (e.g., the cell wall) to equalize concentration differences. Since plant cells have a higher salt concentration than distilled water, water flows in, causing the cell to swell and, in the worst case, burst.
With a conventional substrate for houseplants, the risk is lower than with plants that are completely submerged in water.
Alternative: Descale tap water
If your tap water is very hard but you still want to use it to water your plants, there are several ways to reduce the lime content:
Boiling: When boiling, some of the lime settles at the bottom of the container.
Descaling by letting it stand: If you let the water stand overnight, some of the limescale can settle.
Filtering: With special water filters you can remove limescale and other harmful substances.
