Though aquatic life is generally unaffected by naturally occurring hardness ions, calcium, magnesium, and iron, human water uses are affected by hardness scale and deposits.
Hard water occurs when large amounts of calcium, magnesium, or iron ions are present.
Hard water is also known for many natural wonders such as many rock terraces around mineral-rich hot springs. Aquatic life is also unaffected by the high contents of calcium, magnesium, and iron ions. From the human perspective hard water can be a nuisance. It clogs pipes, water heaters, and leaves water spots on cars. Hard water also gives water an undesirable taste.