Killed my first 3 houseplants with tap water before a guy at the Norfolk botanical swap set me straight
I used to just fill a cup from the sink and dump it on everything, and my calathea and two ferns all went crispy within about 6 weeks. At a plant swap in Norfolk last month, an older guy running a table of pothos cuttings asked what I was watering with and then explained that my city water runs hard, around 9 grains per gallon, and the built up salts were burning my leaf tips. He had me switch to rain water from a bucket on my porch and also let the soil dry a bit more between drinks. Two months in, the ferns are pushing out new fronds and the calathea finally unfurled a leaf without brown edges. The tap water plant still sitting in my kitchen is basically a stump now, which says plenty. Has anyone else dealt with hard water wrecking their tropicals, and did switching to rain or distilled actually fix it for you?
That Norfolk swap guy basically handed you the plant version of a cheat code. One thing nobody mentions is that hard water salts don't just burn the leaf tips, they build up in the soil over time and slowly mess with the pH, which locks out nutrients even after you switch to rain water. So it might be worth flushing your pots a few times with the rain water, like running way more through than normal and letting it drain out the bottom, just to push all that old salt out of the root zone. My ferns perked up way faster once I did that, since the soil itself was still salty for weeks after I changed what was going in the top.