What Water Should You Use for Plants?

Water quality is the most underrated killer in this hobby. It rarely kills a plant outright, which is exactly why it goes unnoticed: the plant declines slowly over months, the owner blames light or humidity or their own thumb, and the actual culprit is sitting in the watering can.

For most tropicals it is a minor factor. For carnivorous plants it is the difference between a plant that thrives and one that is dead by spring.

What is actually in tap water

Tap water carries dissolved minerals, mostly calcium and magnesium salts, measured as total dissolved solids in parts per million. Depending on where you live that can be anywhere from about 50 ppm to well over 500. It also usually carries chlorine or chloramine for disinfection, and in some areas added fluoride.

Plants take up water and leave most of those dissolved solids behind in the growing medium. Every watering adds a little more. Over months the concentration climbs until it starts burning root tips and scorching leaf margins, and by then you are looking at a symptom months downstream of the cause.

Carnivorous plants: mineral free or nothing

This is not a preference, it is a hard requirement. Venus flytraps, Sarracenia, Drosera and Nepenthes evolved in nutrient poor bogs and have no mechanism for coping with dissolved salts. Use distilled, reverse osmosis or collected rain water only, and aim to keep total dissolved solids under roughly 50 ppm.

Tap water will kill a flytrap. Not immediately, which is the trap: the plant looks fine for weeks, then declines through a summer and dies over winter, and the owner concludes carnivorous plants are difficult. They are not difficult. They are specific, and nobody told them.

Spring water and mineral water are worse than tap, not better. The minerals are the problem, and bottled spring water is sold on having more of them.

Tropicals: it matters less, but it still matters

Aroids are far more tolerant. Most Philodendron, Monstera and Syngonium will grow happily on tap water indefinitely. Where you see the difference is at the margins and over time.

Thin leaved and velvet leaved plants show it first. Prayer plants (Calathea, Maranta, Ctenanthe) are notoriously sensitive, and the crispy brown edges people blame on humidity are very often mineral burn instead. Velvet leaved Anthurium mark visibly from hard water. Some plants, including Dracaena and spider plants, are specifically sensitive to fluoride.

If your tap water is soft and you are growing ordinary aroids, carry on. If your water is hard, or you are growing prayer plants or velvet Anthurium, switching is one of the cheapest upgrades available.

Your options, ranked by practicality

• Rain water: free, naturally near zero ppm, and the best option if you can collect it. Collect from a clean surface rather than straight off an old roof, and use it within a week or two before it goes stagnant.
• Distilled: reliably near zero ppm, available in any supermarket, and the simplest answer for a small collection. Gets expensive at volume.
• Reverse osmosis: the right answer for a large collection. A countertop unit pays for itself quickly if you are buying distilled by the gallon.
• Filtered (jug style): the common mistake. A standard carbon jug filter improves taste and removes some chlorine. It does not meaningfully reduce dissolved solids. Filtered tap water is still tap water as far as a flytrap is concerned.
• Left standing overnight: lets chlorine off gas, which helps slightly. Does nothing for chloramine, which most water utilities now use instead, and nothing at all for minerals.

Just measure it

A total dissolved solids meter costs about the price of a cheap plant and removes all the guesswork. Test your tap, test your filtered water, test your rain barrel. Most people are surprised in one direction or the other, and it turns an argument into a number.

Rough guide: under 50 ppm is safe for carnivorous plants. Under 150 ppm is fine for most tropicals. Over 300 ppm and you will see it in sensitive foliage eventually.

Flushing a plant that has been on hard water

If minerals have already built up, water heavily with mineral free water several times in a row, letting it run freely out of the drainage holes to carry the salts away. Repotting into fresh medium does it faster. Do not fertilise while you are flushing, and expect existing damaged leaves to stay damaged: the plant will not repair them, it will grow past them.

What this means for a new plant

A plug or a tissue culture plantlet is at its most vulnerable in the first few weeks, when its root system is small and there is very little plant mass to buffer a mistake. Starting a carnivorous plug on tap water is one of the few genuinely fatal errors you can make on day one.

If you are acclimating tissue culture, every rinse and the peroxide soak should use distilled or RO water too. The full process is in our tissue culture acclimation guide, and the carnivorous specifics are covered in the Nepenthes care guide.

Where to start

Browse carnivorous plugs and tissue culture, or the full range of care guides by variety.