What method is commonly used to soften water?

Ion exchange is a widely used method for softening water, particularly in residential and municipal settings. This process involves exchanging calcium and magnesium ions, which contribute to water hardness, with sodium or potassium ions. As water passes through a resin bed containing sodium or potassium ions, the hardness ions are captured by the resin, effectively reducing the overall hardness of the water.

This method is favored because it is efficient and can be easily regenerated when the ion-exchange capacity is exhausted. Additionally, ion exchange systems can be relatively compact and straightforward to operate, making them suitable for varying scales of water treatment.

In contrast, reverse osmosis involves forcing water through a semi-permeable membrane to remove a wide range of impurities, including hardness ions, but it is not specifically designed for softening. Distillation, while effective for purifying water, involves boiling water and collecting the steam, which also removes hardness but is energy-intensive and less practical for large volumes. Coagulation is a process primarily used to remove suspended solids and impurities from water, rather than addressing water hardness. Thus, ion exchange stands out as the most directly applicable method for softening water.