Pure water production system and pure water production method

A pure water production system, comprising:

• a reverse osmosis membrane device;
• an electric deionized water production device that is connected to an upstream pipe and a downstream pipe, wherein the upstream pipe is configured to receive water to be treated from the reverse osmosis membrane device and carry the water to be treated to the electric deionized water production device, and the downstream pipe is configured to receive and carry treated water that is discharged from the electric deionized water production device;
• a control device that is configured to control a processing condition of the water to be treated that is upstream of the reverse osmosis membrane device;
• and
• a measuring device that is connected to a first sampling line which branches from the upstream pipe and a second sampling line which branches from the downstream pipe, the measuring device being configured to:
• measure a boron concentration of the water to be treated of the first sampling line,
• measure a boron concentration and a specific resistance of the treated water of the second sampling line, and
• calculate a boron removal rate of the electric deionized water production device based on the measured boron concentrations;
• wherein
• based on the calculated boron removal rate that is received from the measuring device, which the control device detects as (i) exceeding a threshold value the calculated boron removal rate, (ii) exceeding a prescribed concentration value of the boron in the treated water of the second sampling line, and/or (iii) exceeding a prescribed specific resistance value of the treated water of the second sampling line, the control device is configured to control at least one of pH, recovery rate, pressure, and temperature of the water to be treated that is upstream of the reverse osmosis membrane device such that:
• the calculated boron removal rate becomes equal to or lower than the threshold value,
• the concentration of the boron in the treated water of the second sampling line becomes equal to or lower than the prescribed concentration value and
• specific resistance of the treated water of the second sampling line becomes equal to or higher than the prescribed specific resistance value.