Water is separated into deuterium-depleted water having a low deuterium concentration and deuterium-enriched water having a high deuterium concentration easily and at low cost.
A method for separating water into deuterium-depleted water and deuterium-enriched water, the method including: adsorbing water vapor on an adsorbent including a pore body having pores 6 while supplying water vapor to and allowing the water vapor to pass through the adsorbent for a predetermined period of time; recovering deuterium-enriched water containing a large amount of heavy water 8 from the water vapor not adsorbed on the adsorbent; and then recovering deuterium-depleted water containing a large amount of light water 7 from the water vapor adsorbed on the adsorbent.