Hard water easy to grow plants? Hmmm first one that comes to mind is Vals. They love hard water. Amazon swords do pretty well in hard water also. But they get BIG FAST. Too big and fast for my liking.
But that aside I have had luck with most plants that I have tried and I have quite hard water here in Hell-A. But you know what? That's the best part of this hobby.... experimentation. Try some plants that you like. They just might take.
Best of luck!