Magnesium is a mineral naturally present in water from rock erosion. It's essential for health but can cause taste issues and scale buildup at high levels.

Magnesium enters water supplies primarily through the erosion of rocks containing magnesium-rich minerals. While essential for human health, high levels can affect water taste and contribute to water hardness. Magnesium is typically measured using atomic absorption spectroscopy or ICP-MS. Water softening systems can reduce magnesium levels, which may be desirable to prevent scale buildup in pipes and appliances. However, completely removing magnesium from drinking water is not necessary or recommended for health reasons.