Which method can be used to lower the hardness of water?

The method to lower the hardness of water is through softening. Water hardness is primarily caused by the presence of dissolved minerals, such as calcium and magnesium ions. Softening water typically involves a process where these hardness-causing ions are exchanged with sodium ions, effectively reducing the total hardness of the water. This is often done using ion-exchange resins in water softeners, which trap calcium and magnesium and replace them with sodium, thus improving the water quality for various uses, including drinking and laundry.

Other methods listed, like chlorination and filtration, do not specifically target the hardness of water. Chlorination is used primarily for disinfection, whereas filtration can remove particulates but does not alter the mineral composition responsible for hardness. Heating water may affect the solubility of certain minerals but does not actively reduce water hardness. Hence, softening is the most appropriate and effective method for addressing this issue.