Hard water and soft water are defining depending on water contaminants with some metals ions such as calcium, magnesium. Hard water is not good for all position; same way soft water also not suitable for all applications.
Generally hard water …
What is soft water
Soft water means when the water is free from the ions of chloride, sulfate and bicarbonate of calcium and magnesium salt or presence little amount of these ions; in particular total water hardness less than 150 …