A water softener for a dishwasher includes a tank body having a regeneration tank that accommodates brine, an exchange tank that accommodates an ion exchange resin, and a flow path configured to supply water to the regeneration tank and the exchange tank. The water softener further includes a regeneration inlet in communication with the regeneration tank, an exchange inlet in communication with the exchange tank, and a switching valve mounted at the tank body and configured to open and close the regeneration inlet and the exchange inlet to switch the flow path. The switching valve includes a head configured to open and close the regeneration inlet and the exchange inlet. A sealing protrusion protrudes toward the head from a circumference of the regeneration inlet and is configured to contact the head to seal the regeneration inlet.