Where are you reading this from? I grow plants fine in my (hard) water.
Some of our plants seem to be fine. But the dwarf hairgrass didn't last long. It's hard to tell if it died off because of the water or because of the snails though. The banana plant is certainly thriving.
As to where I've read this I'm afraid I can't provide those details. I've read so much from so many places that I can't possibly remember where each tidbit came from. Sadly, this hobby is so rife with myth and misinformation that you can find any answer you want to any question you have.