The present invention relates to a water treatment apparatus, and more specifically, to a water treatment apparatus which is constructed to purify contaminated air and raw water through generation of ozone and active oxygen by installing ultraviolet lamps with different ultraviolet wavelength bands within multistage chambers. The water treatment apparatus according to the present invention comprises: a first reaction chamber (10) which is formed to exhaust external air to an outlet (14) formed in an upper end of the other side of the first reaction chamber (10) by introducing the external air to an external air inlet (12) through an external air blowing unit (15), and which has an ultraviolet lamp (16) with a short wavelength of 100 to 290 nm installed at the center of the inner side thereof such that microorganisms and harmful organic materials included in the air are oxidized and decomposed by ozone generated by exposing the introduced external air to ultraviolet rays a second reaction chamber (20) which is connected to the first reaction chamber (10) such that harmful organic materials included in the raw water are oxidized and decomposed by ozone generated in the first reaction chamber (10) as purified air is being introduced to one side of a lower end of the second reaction chamber (20) and as the introduced purified air is being aerated in an upward direction from the bottom side of raw water introduced, and which has an ultraviolet lamp with a medium wavelength of 290 to 320 nm installed at the center of the inner side thereof such that the residual ozone is converted into superoxide ions by irradiating ultraviolet rays onto residual ozone and a third reaction chamber (30) which is connected to the second reaction chamber (20) and has an ultraviolet lamp (36) with a long wavelength of 320 to 400 nm installed at the center of the inner side thereof to sterilize bacteria included in the raw water, oxidize and decompose harmful organic materials included in the
