PURPOSE: To easily decompose and remove the total org. halogen compds. in water subjected to a chlorine treatment in a short period of time by subjecting water to be treated of 10°C (low temp. side)-50°C (high temp. side) to irradiation of 254nm UV rays for a prescribed period of time, thereby decomposing variant protists.

CONSTITUTION: The water to be treated of 10-50°C is irradiated by 254nm UV rays. More specifically, a UV sterilizing lamp of 12watt is installed in a glass jacket 2 of the water treatment device 1 and 15l water to be treated is injected into the device and is irradiated by the UV rays for 5minutes by varying the water temp. As a result, the org. halogen compds. by the UV rays are gradually treated from 5°C water temp. The removal rate is about 20% at 10°C water temp. The highest value of the removal rate is obtd. in the 28-40°C water temp. range. The removal rate is about 20% at 50°C water temp. All the org. halogen compds. are removed by this method without requiring a large device.