How to measure the conductivity of 18.2 ultrapure water

The ultra-pure water of 18.2 can't be detected by conductivity, and the ultra-pure water of 18.2 is monitored online with a resistance meter, which has high accuracy. The unit monitored by conductivity meter is (μs/cm), and the unit monitored by resistivity meter is (mω cm/cm), so ultrapure water cannot be detected by conductivity meter and can only be converted.