With an ec-meter (conductivity meter) you easily can measure the conductivity of the water. Ideal to know if te conductivity of the water is right or that the filter of the osmosis devise isn't full yet etc. Very easy to use.
This meter is an ec meter, tds meter and thermometer in 1. Measures the hardness in microsiemens and in ppm. Measures the temperature in Celsius and Fahrenheit.