Question: I use tap water to water all my houseplants, but I’ve heard that’s not always a good idea. What difference does it make?
Garden author Barbara Pleasant talks about water problems in her book, The Complete Houseplant Survival Manual. She says most plants prefer “soft” water, which contains low amounts of calcium and magnesium salts, over “hard” water, which contains high amounts of these elements. Water softeners remove the mineral salts through filtration or magnetization, but the water still contains high levels of salt, she says. This could lead to problems when it is used to water plants.
Pleasant suggests using rainwater or bottled distilled water, which are naturally soft, on your indoor plants.
The mineral salts in tap water are only one thing to consider. Plants may also be sensitive to too much chlorine, which is added to tap water to prevent bacteria, and some plants, including palms and dracaenas, are sensitive to fluoride.
To solve the problem of too much chlorine, allow the water to sit out overnight, so that chlorine and other chemicals escape into the air. If you suspect fluoride may be causing a problem (browning leaf tips on plants may be a clue), it may help to add a pinch of lime on the surface of the pot every few months, Pleasant advises. “This helps raise the pH of the soil, which makes the fluoride more soluble in water.
One other watering tip: whatever the source of the water, make sure it’s at room temperature when you water your plants. Drenching a houseplant in icy water chills the roots, which can cause them to rot, Pleasant says.