Total Dissolved Solids (TDS) Calculator

About the Total Dissolved Solids (TDS) Calculator

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.

When This Page Helps

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.

How to Use the Inputs

1. Enter the electrical conductivity of your water sample in μS/cm (or mS/cm).
2. Select the appropriate TDS conversion factor for your water type.
3. Alternatively, enter TDS directly in mg/L (ppm) if you have a gravimetric measurement.
4. Review the calculated TDS, classification, and drinking standard compliance.
5. Optionally enter individual ion concentrations for a detailed mineral profile.
6. Use the treatment comparison section to evaluate filtration options.
7. Check the water use suitability table for irrigation, brewing, and aquarium guidance.

Example Calculation

Tips & Best Practices

• Calibrate your TDS/EC meter with standard solutions (84 μS/cm and 1413 μS/cm are common).
• Temperature affects conductivity — most meters auto-compensate to 25 °C.
• RO membranes typically remove 95-99% of TDS; carbon filters remove organic TDS but not minerals.
• For brewing coffee, the SCA recommends 75-250 mg/L TDS in brewing water.
• Rising TDS in a closed system (e.g., fish tank) indicates insufficient water changes.
• Municipal water reports list TDS — compare yours against the source report for meter accuracy.

TDS Classification for Drinking Water

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.

Treatment Options

**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.

Water Source Typical 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.

Frequently Asked Questions

• What is an acceptable TDS level for drinking water?

  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.

• How do I measure TDS?

  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.

• Why does the conversion factor vary?

  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.

• Is low TDS water harmful?

  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.

• What is the relationship between TDS and hardness?

  Hardness measures Ca²⁺ and Mg²⁺ specifically, while TDS includes all dissolved species. Hardness is typically 40-60% of TDS in natural waters.

• Can I use TDS to assess pool or aquarium water?

  Yes. Pools typically run 1000-2000 ppm. Freshwater aquariums: 100-300 ppm for most tropical fish. Marine tanks: ~35,000 ppm (seawater salinity).