Is a device which helps control the TDS level of the water coming out of the RO. The RO process reduces the hardness of the input water by approximately 90%. This means, that for an input of TDS 700, the output will be close to 70.However, sometimes the source being used for the RO system itself has a low TDS value. Now water having a low TDS value, does not indicate that its pure. Also, the RO system does not just reduce the TDS, it also filters away, microbes and other contaminants from the water. Thus the water coming from such a set up, with a low input TDS, with have a bitter taste. To prevent this, a TDS controller is installed which allows us to raise the TDS value of the output water.