Water has some pretty amazing properties. One of them is that it will erode and dissolve minerals and pick them up in its stream. This is why you sometimes will be dealing with hard water as a homeowner. Usually, this comes from water that has run through a layer of limestone or similar minerals, and it will cause the water to have a high concentration of calcium in it.
While calcium actually is good for our bodies and harmless to ingest in the concentrations that you will find in hard water, it is not quite the same for your pipes and fixtures. You can sometimes see a buildup of calcium on faucets and showerheads in a home that has a problem with hard water. While these issues can be resolved fairly easily, it is a lot worse if there is buildup inside of your pipes or in your water heater. It might be necessary for you to get a system that will soften the water for you.
