Abstract: A TOC monitor for determining the quality of ultrapure water is described. The TOC monitor includes a ultraviolet oxidizer in the form of spiral tubing, having an inlet connected to a first resistivity meter and an outlet to a second resistivity meter. The difference between the measured resistivity values provides an indication of the total amount of organic carbons present in the water. Each resistivity meter includes an outer tubular electrode and an inner cylindrical electrode extending therethrough. A narrow annular space is formed therebetween for increased flow of the water, permitting an accurate measurement even at very low flow rates. Such TOC monitors are used in a ultrapure water production plant to continuously monitor the quality of water. The plant can produce ultrapure water in a continuous process and accordingly dispense with costly and contaminants producing reservoirs.