Water quality
Also known as Tap water for plants, Rainwater, Distilled and RO water
In short
Most plants cope with ordinary tap water, but some are sensitive. Softened water adds sodium, hard water can raise pH, fluoride causes tip burn on sensitive plants, and carnivorous plants need very low-mineral water. Rainwater, distilled or reverse-osmosis water avoid most of these problems.
How it looks
Signs your water may be a factor: white or crusty mineral deposits on the mix surface, pot rims or terracotta walls; brown tips and margins on fluoride-sensitive plants such as Dracaena and spider plant; decline of carnivorous plants watered with tap water. A cheap TDS (total dissolved solids) meter measures how much is dissolved in the water.
Signs
Brown, dead leaf tips and margins, white crusts, gradual yellowing on acid-loving plants in hard-water areas, blackening traps and poor growth in carnivorous plants.
What favours it
Problems build up over time in containers because dissolved minerals and fertiliser salts accumulate in the mix, especially when pots are never flushed. Fluoride accumulates at leaf tips and margins through the transpiration stream.
Prevention
- Avoid water from a water softener; it contains more dissolved salts (sodium).
- Leach pots every 4–6 months by running at least twice the pot's volume of water through the mix.
- For fluoride-sensitive plants (Dracaena, spider plant), use rain, distilled or reverse-osmosis water; the PNW Plant Disease Handbook also suggests keeping mix pH around 6.5–7 with adequate calcium and fertilising sparingly.
- For carnivorous plants, the ICPS advises tap water only if its TDS is below about 90 ppm; otherwise use distilled, reverse-osmosis or clean rainwater. Ordinary filters do not remove dissolved salts.
- Rainwater suits acid-loving (ericaceous) plants in hard-water areas.
- Use water at room temperature.
Treatment
Start with the first step and move down only if the problem persists.
- Trim off brown tips if you like; damaged tissue will not turn green again.
- Flush the mix with plenty of low-mineral water or repot into fresh mix if salt crust is heavy.
- Switch sensitive plants to rain, distilled or RO water.
Pros and cons
Pros
- Rainwater: free where it can be collected, low in minerals.
- Distilled/RO water: very low in dissolved solids, ideal for carnivorous plants.
Cons
- Distilled and RO water cost money or equipment; very pure water contains no nutrients, so other plants still need feeding.
- Stored rainwater needs clean gutters and a water butt cleaned regularly; the RHS notes dirty stored water can carry root-rot organisms such as Pythium and Phytophthora.
Look-alikes
- Salt and fertiliser burn
- Over-fertilising causes the same brown tips; check your feeding as well as your water.
- Low-humidity damage
- Dry air also browns leaf tips and edges; compare with plants watered differently.
Typical uses
Sensitive groups: carnivorous plants, Dracaena, spider plant (Chlorophytum), and acid-loving plants in hard-water areas.
Related
Sources
- Watering Indoor Plants — University of Maryland Extension
- Watering — Houseplants, University of Illinois Extension
- Dracaena-Tip Burn — Pacific Northwest Plant Disease Management Handbook
- Growing Dionaea muscipula — International Carnivorous Plant Society
- Collecting, storing and reusing water — RHS
Written in our own words from these sources. Check a product label before using any treatment.