A method for capturing atmospheric water vapor during the night, relative humidity is high, is discussed. A liquid into which calcium chloride is dissolved is allowed to soak into the water-retentive material's pores, which causes the water vapor pressure at the boundary to drop and thereby produces water absorption because of the difference in water vapor pressure with the surrounding area. Experimental results show water absorption status of a solid sample that consists of ceramics with pores containing calcium chloride and allowed to sit for six hours at 95% relative humidity. It has not reached the stage of practical application as water absorbent during the summer season, but it can he made into an ideal system to recapture at night the water that is lost due to daytime evaporation, and it is harmlessto human health if not leached in great quantities.