For most houseplants, ordinary tap water is fine. A few details are worth knowing, though.
Never use water from a household water softener. Softeners swap minerals for sodium salts, and the RHS describes that water as highly toxic to plants. Chlorine is less of a worry: leaving tap water in an open container for a day lets it escape, and it also brings the water to room temperature. That trick does not remove fluoride. Some plants, notably corn plant (Dracaena fragrans) and other dracaenas, are sensitive to fluoride and show brown, dead leaf tips; rainwater or reverse-osmosis water avoids it. Acid-loving plants and carnivorous plants also prefer rainwater or distilled water over hard tap water.
Every kind of water and fertiliser leaves some dissolved salts behind as the mix dries. Over months they build up, showing as a white crust on the mix or pot rim, brown leaf tips and slower growth. The fix is leaching: every four to six months, run plenty of water through the pot, at least twice the pot's volume, and let it drain away. The University of Maryland also suggests leaching newly bought plants.
Key points
- Never water with softened water.
- Standing tap water overnight clears chlorine, not fluoride.
- Flush pots with at least twice their volume of water every few months to wash out salts.
Try this
Look at the rims of your pots and the surface of the mix for a white crust. If you find one, leach that pot in the sink with plenty of water today.
Check yourself
Read more in the reference
Sources
Marking a lesson done is kept on this device only.