An apparatus for reducing regenerant and wastewater by compressed air, characterized in that the apparatus comprises: a resin tower having an upper opening and a lower opening opposite the upper opening, and packed with a resin material including strong acid cation exchange resin, weak acid cation exchange resin, strong base anion exchange resin, weak base anion exchange resin, selective ion exchange resin, chelating resin, or adsorber resin; a waste fluid/tap water tank connected with the upper opening or the lower opening of the resin tower, so as to unidirectionally supply waste fluid/tap water to the resin tower; a compressed air supply connected with the upper opening of the resin tower, so as to unidirectionally supply compressed air to the resin tower; a regenerant tank connected with the upper opening and the lower opening of the resin tower, so as to bidirectionally supply fresh regenerant to the resin tower and to drain spent regenerant from the resin tower; a pure water tank connected with the upper opening and the lower opening of the resin tower, so as to unidirectionally supply pure water to the resin tower; a wastewater treatment tank connected with the upper opening and the lower opening of the resin tower, so as to unidirectionally drain wastewater out of the resin tower; a regenerant recovery tank connected with the upper opening of the resin tower, so as to unidirectionally drain spent regenerant from the resin tower; a collection tank connected with the regenerant recovery tank; a rinse water collection tank connected with the upper opening and the lower opening of the resin tower, so as to bidirectionally supply collected rinse water to the resin tower and to drain the rinse wastewater from the resin tower. a resin tower having an upper opening and a lower opening opposite the upper opening, and packed with a resin material including strong acid cation exchange resin, weak acid cation exchange resin, strong base anion exchange resin, weak base anion exchange resin, selective ion exchange resin, chelating resin, or adsorber resin; a waste fluid/tap water tank connected with the upper opening or the lower opening of the resin tower, so as to unidirectionally supply waste fluid/tap water to the resin tower; a compressed air supply connected with the upper opening of the resin tower, so as to unidirectionally supply compressed air to the resin tower; a regenerant tank connected with the upper opening and the lower opening of the resin tower, so as to bidirectionally supply fresh regenerant to the resin tower and to drain spent regenerant from the resin tower; a pure water tank connected with the upper opening and the lower opening of the resin tower, so as to unidirectionally supply pure water to the resin tower; a wastewater treatment tank connected with the upper opening and the lower opening of the resin tower, so as to unidirectionally drain wastewater out of the resin tower; a regenerant recovery tank connected with the upper opening of the resin tower, so as to unidirectionally drain spent regenerant from the resin tower; a collection tank connected with the regenerant recovery tank; a rinse water collection tank connected with the upper opening and the lower opening of the resin tower, so as to bidirectionally supply collected rinse water to the resin tower and to drain the rinse wastewater from the resin tower.