Which water characteristic relates to the calcium and magnesium content of water?

• A. Alkalinity
• B. Acidity
• C. Dissolved Gases
• D. Hardness

Answer: (D)

Water hardness is the property that reflects how much calcium and magnesium are dissolved in the water. The presence of Ca2+ and Mg2+ ions makes water hard—the more of these ions, the harder the water. This is often reported as calcium carbonate equivalents because it’s a convenient way to compare hardness levels. There are two parts: temporary hardness, from bicarbonate salts that can be removed by boiling, and permanent hardness, from sulfates and chlorides of calcium and magnesium that don’t go away with boiling. Hard water matters because it causes soap to not lather well and leads to scale buildup in pipes and boilers, which is why treating or managing hardness is common in water systems. Alkalinity relates to buffering capacity from bicarbonates, carbonates, and hydroxides; acidity is about hydrogen ion concentration and pH; dissolved gases involve gases like CO2 and O2 and don’t determine calcium or magnesium content.