Total Dissolved Solids: Water Quality
TDS = total dissolved solids (ppm or mg/L). TDS ≈ k × EC (conductivity). EPA <500 ppm, WHO <1000 ppm for drinking water. Hardness = 2.497×Ca²⁺ + 4.118×Mg²⁺ as CaCO₃.
Why This Chemistry Calculation Matters
Why: TDS indicates water purity. High TDS: taste, scaling, health. EPA/WHO set drinking water limits. Conductivity provides quick estimate.
How: Enter conductivity (μS/cm) and factor (0.5-0.7), or sum ion concentrations. TDS ≈ k × EC. Hardness from Ca²⁺, Mg²⁺.
- ●TDS ≈ 0.5–0.7 × EC (μS/cm).
- ●EPA <500 ppm; WHO <1000 ppm.
- ●Hardness as CaCO₃ equivalent.
Compact Examples
Inputs
⚠️For educational and informational purposes only. Verify with a qualified professional.
🔬 Chemistry Facts
TDS ≈ k × EC. k = 0.5–0.7 typically.
— ASTM
EPA secondary max 500 ppm TDS.
— EPA
Hardness = 2.497×Ca + 4.118×Mg (mg/L as CaCO₃).
— Water chem
Gravimetry is definitive; conductivity estimate.
— ASTM D5907
📋 Key Takeaways
- • TDS | Total dissolved solids in ppm or mg/L
- • TDS ≈ k × EC | Conductivity (μS/cm) × factor 0.5–0.7
- • EPA < 500 ppm | WHO < 1000 ppm for drinking water
- • Hardness | 2.497×Ca²⁺ + 4.118×Mg²⁺ (mg/L as CaCO₃)
Did You Know?
TDS meters estimate from conductivity; lab gravimetry is definitive.
Source: ASTM D5907
Marine aquariums need ~35,000 ppm TDS; freshwater 200–400 ppm.
Source: Aquarium
Hydroponics: seedlings 400 ppm, vegetative 800 ppm, flowering 1200 ppm.
Source: Hydroponics
EPA secondary MCL 500 ppm; WHO guideline 1000 ppm.
Source: EPA/WHO
Conversion factor k varies with ion composition (0.5–0.7).
Source: Water chem
Pool TDS: ideal 1500 ppm; drain when > 3000 ppm.
Source: Pool care
How the TDS Calculator Works
Enter conductivity (μS/cm), TDS value, or ion concentrations. TDS = k × EC or sum of ions; hardness from Ca²⁺ and Mg²⁺.
From Conductivity
TDS (ppm) = k × EC (μS/cm)
From Ions
TDS = Σ Ca²⁺ + Mg²⁺ + Na⁺ + K⁺ + Cl⁻ + SO₄²⁻ + HCO₃⁻ + ...
Expert Tips
Use Correct k
0.5 general; 0.65 well water; 0.7 brackish.
Calibrate
TDS meters use conductivity; calibrate regularly.
Temperature
EC varies with T; measure at 25°C or compensate.
Water Type
Select drinking, aquarium, hydroponics, or pool.
Water Quality Standards
| Source | Standard | Value | Description |
|---|---|---|---|
| EPA | Secondary Maximum Contaminant Level | 500 ppm | Aesthetic standard for drinking water |
| WHO | Guideline Value | 1000 ppm | Acceptable for drinking water |
| WHO | Excellent | 300 ppm | Excellent quality drinking water |
| EPA | Excellent | 50 ppm | Excellent quality drinking water |
| Aquarium | Freshwater | 400 ppm | Ideal for most freshwater fish |
| Aquarium | Marine | 35000 ppm | Ideal for saltwater aquariums |
Frequently Asked Questions
What is TDS?
Total dissolved solids — sum of all inorganic and organic substances in water, typically in ppm or mg/L.
How to convert EC to TDS?
TDS ≈ k × EC (μS/cm). k = 0.5–0.7 depending on water composition.
EPA vs WHO TDS limits?
EPA secondary MCL 500 ppm; WHO guideline 1000 ppm for drinking water.
Why does conversion factor vary?
Different ions have different conductivity per mass; ion mix affects k.
TDS vs hardness?
TDS = total dissolved; hardness = Ca²⁺ + Mg²⁺ as CaCO₃ equivalent.
Is low TDS safe?
TDS < 50 ppm is excellent; very low TDS may lack minerals but is generally safe.
Hydroponics TDS?
Seedlings 400 ppm; vegetative 800 ppm; flowering 1200 ppm.
Key Numbers
📚 Official Sources
⚠️ Disclaimer: TDS values are estimates. EPA/WHO guidelines are guidelines. For regulatory compliance use certified lab methods (ASTM D5907).