TDS = Residue Mass / Sample Volume × 10⁶ (mg/L)
TDS measures all inorganic and organic substances dissolved in water — minerals, salts, metals, cations, anions. It's measured by evaporating a known volume of filtered water and weighing the residue (gravimetric method) or estimated from electrical conductivity (TDS ≈ EC × 0.5 to 0.7). WHO drinking water guideline: TDS < 600 mg/L is acceptable; > 1000 mg/L is unpalatable. Typical TDS values: distilled water 0-5, rainwater 5-30, tap water 100-500, seawater ~35,000 mg/L. High TDS indicates hardness, scaling potential, and possible contamination. TDS is a key parameter in: drinking water quality, irrigation water management, wastewater treatment, aquarium maintenance, and industrial process water specifications.