TDS Meter is a portable digital tool that measures the total dissolved salts and minerals in water. It is used to check the quality of drinking water, the effectiveness of reverse osmosis filters, and for agriculture, with readings displayed in parts per million (ppm). Correct Usage Method Bring a clean cup and fill it with the water to be tested. Turn on the device and immerse the metal probe (the bottom part only) in the water. Wait a few seconds for the reading to stabilize on the screen. Press the Hold button to save the reading if necessary, then rinse and dry the probe.