carbon treatment section 10 and the capacitive de ionization treatment section 100 organic matter content measurement sections 12 and 13 for measuring the total organic carbon concentration toc in water are installed respectively the process of a water treatment using the above water treatment device will be described hereinafter the following will describe as an example the case where the water treatment device includes an oil separator and a separation section and treats industrial waste water the pretreatment section 2 receives raw water waste water in the case of waste water from a plant or domestic waste water the water contains as organic components oils in the form of oil droplets or an emulsion as well as organic matters that are present in water in the form of molecules or ions acetic acid formic acid phenol etc the oil separator removes oils form the raw water the separation section adds a chelating agent to waste water to chelate heavy metals and insolubilize them the separation section adds an aggregating agent to waste water to cause the aggregation of heavy metal chelates suspended particles etc followed by sedimentation thereby removing heavy metals and suspended particles from the waste water in the case of configuration having a biological treatment section the waste water from which oils heavy metals and suspended particles have been removed is fed to the biological treatment section in the biological treatment section organic matters such as acetic acid formic acid humic acid and phenol as mentioned above are decomposed in the case of configuration having an oxidization treatment section.