In this project, we will learn how to make our own IoT Based TDS Meter using NodeMCU ESP8266 & TDS Sensor for Water Quality Monitoring. The TDS value (Total Dissolved Solids) gives the sum of dissolved solids in water. These solids include for instance salts, minerals, and conductive metals ions. The value is additionally called the conductivity of the water. Because the more such solids or ions are within the water, the higher it conducts electricity. TDS meters typically quantify this conductivity in micro siemens or ppm. The latter stands for parts per million, i.e. the number of solid particles per a million water mixture particles. The value of 40 ppm means from a million particles there are 40 dissolved ions and therefore the rest (= 999 960) are water molecules.