Calculate TDS from conductivity, estimate water hardness, compare mineral content against drinking standards, and convert between TDS units for water quality analysis.
Total Dissolved Solids (TDS) measures the combined content of all inorganic and organic substances dissolved in water. Expressed in milligrams per liter (mg/L) or parts per million (ppm), TDS is one of the most important indicators of water quality for drinking, agricultural, industrial, and aquarium applications.
TDS is most commonly estimated from electrical conductivity (EC) using a conversion factor that depends on the type of dissolved minerals. Pure NaCl solutions use a factor around 0.5, while mixed mineral waters use 0.55-0.7. Direct gravimetric measurement (evaporating and weighing residue at 180 °C) is the definitive method.
This calculator converts between conductivity and TDS, compares your water against WHO, EPA, and EU drinking standards, estimates the contributions of individual ions, and provides guidance for water treatment technologies — reverse osmosis, distillation, deionization, and carbon filtration.
For best results, combine calculator output with direct observation and periodic check-ins with a veterinarian or qualified advisor. Small adjustments made early usually improve comfort, safety, and long-term outcomes more than large corrective changes made later.
Quick, reliable TDS estimation is essential for water utilities, well-water homeowners, coffee and beer brewers, aquarium hobbyists, and agricultural irrigators. This calculator replaces guesswork with standard-based assessments and treatment recommendations. It also makes it easier to spot changes over time before taste, equipment, or livestock issues become costly and operationally disruptive.
TDS (mg/L) = EC (μS/cm) × Conversion Factor. Typical factors: 0.50 (NaCl), 0.55 (mixed), 0.65 (natural water), 0.7 (high sulfate). 1 ppm = 1 mg/L = 0.001 g/L. Hardness (mg/L as CaCO₃) ≈ TDS × 0.5 for typical well water.
Result: 520 mg/L (ppm)
An EC reading of 800 μS/cm with a factor of 0.65 gives TDS = 800 × 0.65 = 520 mg/L, classified as "Good" drinking water by WHO standards.
The World Health Organization categorizes drinking water TDS as follows:
| TDS (mg/L) | Rating | |------------|--------| | < 300 | Excellent | | 300 – 600 | Good | | 600 – 900 | Fair | | 900 – 1200 | Poor | | > 1200 | Unacceptable |
Water above 1000 mg/L is generally unpalatable. Above 2000 mg/L it can cause gastrointestinal issues.
**Reverse Osmosis (RO)** removes 95-99% of dissolved solids and is the most effective household treatment. **Distillation** achieves similar purity but consumes more energy. **Deionization (DI)** exchanges cations and anions for H⁺ and OH⁻, producing ultrapure water for lab use. **Activated carbon** removes organic TDS and chlorine but does not reduce mineral TDS.
Rainwater typically has 5-30 mg/L TDS. Mountain streams: 50-100 mg/L. Treated municipal water: 100-400 mg/L. Deep wells: 200-2000 mg/L. Seawater: ~35,000 mg/L. Brine: >100,000 mg/L.
WHO considers <300 mg/L excellent, 300-600 good, 600-900 fair, and >900 poor. The EPA secondary standard is 500 mg/L. Taste is generally acceptable below 600 mg/L.
The easiest method is a TDS meter (actually measures EC and converts). The reference method is gravimetric: evaporate a known volume at 180 °C and weigh the residue.
Different ions have different mobilities and equivalent weights. NaCl solutions conduct more efficiently per mg than CaSO₄ solutions, so the factor depends on the mineral composition.
Water with very low TDS (<50 mg/L) can taste flat and may be corrosive to pipes. However, distilled and RO water are safe to drink; essential minerals are obtained from food.
Hardness measures Ca²⁺ and Mg²⁺ specifically, while TDS includes all dissolved species. Hardness is typically 40-60% of TDS in natural waters.
Yes. Pools typically run 1000-2000 ppm. Freshwater aquariums: 100-300 ppm for most tropical fish. Marine tanks: ~35,000 ppm (seawater salinity).