Water softeners work to replace the calcium and magnesium in water with sodium. This is good news for you because calcium and magnesium make water hard, but not such good news for your plants because calcium and magnesium are important nutrients for them, whereas sodium can harm plants. If high sodium levels build up in houseplant soil, it could eventually damage the plant's roots and cause browning of leaf edges. But if watering your plants with softened water is your only option, you can take steps to lessen the effects of using softened water on your houseplants.
Make sure all plants watered with softened water are potted in pots with holes in the bottom. Consider placing a layer of gravel at the bottom of each pot to promote good drainage.
Hold a potted plant over a sink or laundry tub. Pour in lukewarm water until it runs rapidly out of the drain holes. Though this method adds salts from softened water, it also flushes salts out, creating minimal net salt gain.
Set the plant down and allow several minutes for excess water to drip out. Return the plant to its saucer.