Total dissolved solids (TDS) measurements are crucial for desalination processes, as they affect water quality, operational efficiency, and environmental sustainability. This paper presents a novel solution that uses a differential pressure (DP) transmitter to measure TDS in desalination plants. The proposed method uses a dual-leg setup, with one leg filled with distilled water as a reference and the other with saline water (sample). The DP transmitter measures the pressure difference between the two legs, which indicates the density difference caused by dissolved salts in the sample water. The conversion of pressure difference to density difference and subsequently to TDS offers high accuracy, with an uncertainty of ±521 mg/L (about 1.3%), a significant improvement over existing laboratory measurements used in the desalination plant, which show a variance ranging from 2.7% to 20%. This system enhances operational efficiency and reduces the time required for TDS measurement compared with traditional laboratory methods.