Hard water can be a soap scum and plumbing-fixture nuisance, it’s not dangerous. Calcium and magnesium are essential nutrients that don’t pose a public health hazard.
The white or brown build up around the faucet is calcium carbonate and small amount of other metals such as magnesium. The whiter it is the more calcium, the browner the more metals from other dissolved metals.
Water is a good solvent and as it travels through the ground it dissolves the natural occurring calcium. The calcium (hardness) is not a health hazard and is not deemed a contaminant.