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Hard water is water that has a high mineral content (water with a low mineral content is known as soft water). This content usually consists of high levels of metal ions, mainly calcium (Ca) and magnesium (Mg) in the form of carbonates, but may include several other metals as well as bicarbonates and sulfates. It is not generally dangerous. The simplest way to determine if water is hard or soft is the lather/froth test. If the water is very soft, soap will tend to lather up easily when agitated, where as with hard water it will not. Toothpaste will also not froth well in hard water. More exact methods of 'hardness' detection use a wet titration method to determine hardness.