Taichung, Taiwan-based Savant Electronics’ RT750 mini-total dissolved solids (TDS) meter is designed to assist residential reverse osmosis (RO) water purifier users to quickly check water quality. It’s a cheap and quick tool for end users to monitor their daily drinking water quality. The judge level of the meter is 40 parts per million (ppm). The red light will turn on when the TDS level of the tested water is over 40 ppm. The judge level is also an option from 10 to 150 ppm.