Hard water gets its hardness from the minerals it picks up as it travels through the ground. Specifically, as water percolates through rock, sand, and soil, it dissolves naturally occurring minerals, primarily calcium and magnesium. These minerals, along with others like carbonates, increase the water's mineral content, making it "hard."
The Process of Hard Water Formation
- Rainfall: Rainwater, initially pure, begins its journey.
- Percolation: As rainwater seeps through the ground, it interacts with various geological formations.
- Dissolution: The slightly acidic nature of rainwater helps dissolve minerals like calcium and magnesium from rocks such as limestone, chalk, and gypsum. These minerals are released into the water.
- Mineral Accumulation: The longer the water travels underground, the more minerals it dissolves, leading to increasing hardness.
- Groundwater & Surface Water: This mineral-rich water eventually becomes part of groundwater supplies or flows into surface water sources.
- Municipal Water Supply: This hard water can then be drawn into municipal water systems, supplying homes and businesses.
The concentration of these dissolved minerals determines the degree of water hardness. Higher concentrations mean harder water. The U.S. Geological Survey provides general guidelines for classifying water hardness based on milligrams per liter (mg/L) of calcium and magnesium. Other metals can also contribute to water hardness. As stated by the City of Manhattan Beach, "Water that is considered to be “hard” is high in dissolved minerals, specifically calcium and magnesium." The Department of Energy further explains that "Before reaching the municipal supply, water absorbs mineral content from rocks and soil. Some of this content, like calcium and magnesium, are hard minerals."
Examples of Hard Water Sources:
- Areas with extensive limestone deposits typically have harder water.
- Water drawn from deep wells often has higher mineral content than surface water.
