There disclosed a water reuse method in which a surfactant is easily removed from surfactant-including for-treatment water in a cleaning device, whereby water can be reused, and an adsorbent can easily be regenerated only by exposing the adsorbent to an electrolytic solution, and a washing machine including the function. The method includes a surfactant adsorption treatment step of performing a treatment to adsorb and remove a surfactant in surfactant-including for-treatment water such as cleaning water and rinse water used in a washing machine W by hydrotalcite as an anion exchanger or zeolite as a cation exchanger, and a water reuse step of using, in the washing machine W, the for-treatment water treated in the surfactant adsorption treatment step.