TDS (Total Dissolved Solids)

Total Dissolved Solids (TDS) is the combined measure of all dissolved inorganic and organic substances in water. It is typically reported in **parts per million (ppm)** or milligrams per litre (mg/L), the two units are equivalent for water. TDS reference points for the Indian context: - **Borewell water (avg):** 600–1,800 ppm - **Borewell, Rajasthan / dry zones:** 1,800–3,500 ppm - **Municipal piped water:** 200–600 ppm - **Glacier-fed water (Uttarakhand, HP):** 80–250 ppm - **BIS limit for Packaged Drinking Water (IS 14543):** 50–250 ppm TDS is measured using a calibrated TDS meter (conductivity-based). For BIS compliance, the lab must hold a calibration certificate (NABL ideally) and run daily checks. Plants in high-TDS regions need **twin-pass RO** to consistently hit the 50–250 ppm target.