What is Water Hardness?
Water hardness refers to the amount of dissolved mineral ions, primarily calcium (Ca²⁺) and magnesium (Mg²⁺), present in water. These minerals are typically picked up as water percolates through rock and soil containing limestone, chalk, or gypsum. Hard water is not considered harmful for consumption, but it can cause various issues in households and industrial settings due to its reactive mineral content.
Types and Causes of Hardness
There are two main types of water hardness: temporary and permanent. Temporary hardness is caused by dissolved bicarbonate minerals (calcium bicarbonate and magnesium bicarbonate) and can be removed by boiling the water, which precipitates the minerals as scale. Permanent hardness is caused by calcium and magnesium sulfates, chlorides, and nitrates, and cannot be removed by boiling. These minerals are stable at high temperatures and require other treatment methods for removal.
Practical Effects and Challenges
The presence of high mineral concentrations in hard water can lead to several practical problems. In homes, it often results in 'limescale' buildup in pipes, kettles, and water heaters, reducing efficiency and lifespan of appliances. It also reacts with soap to form soap scum, making it harder to lather and leaving residues on dishes, clothes, and skin. In industrial applications, hard water can cause significant operational issues and increased maintenance costs due to scaling in machinery.
Measurement and Mitigation
Water hardness is typically measured in parts per million (ppm) of calcium carbonate (CaCO₃) or grains per gallon (gpg). Soft water has less than 60 ppm, moderately hard 60-120 ppm, hard 120-180 ppm, and very hard over 180 ppm. Mitigation strategies include water softening systems, which often use ion exchange resins to replace calcium and magnesium ions with sodium or potassium ions, or reverse osmosis for more comprehensive mineral removal.