⛲According to the guidelines of the European Union and the World Health Organization, what is the maximum allowable TDS limit for measuring water hardness?
👉 The European Drinking Water Directive (2020/2184/EU) does not set a maximum limit for the hardness of water nor for the total dissolved solids (TDS).
🔹 Hardness
- Hardness mainly comes from calcium (Ca²⁺) and magnesium (Mg²⁺).
- The EU does not consider it dangerous to health, so there is no “maximum allowable limit.
- Defines only aesthetic / functional limits: very hard water creates salts, while very soft can cause pipe corrosion.
🔹 TDS (Total Dissolved Solids)
- The EU does not set a maximum legal limit for TDS.
- The WHO (World Health Organization) provides guideline taste values:
- <300 mg/L → Excellent quality
- 300–600 mg/L → Good quality
- 600–900 mg/L → Acceptable
- 900–1200 mg/L → Poor quality
- >1200 mg/L → Generally unsuitable for drinking due to taste
✅ Conclusion:
- There is no “maximum allowable limit” from the EU for TDS or hardness.
- There are aesthetic / practical limits. For good drinking water, TDS < 600 mg/L and hardness up to ~250–300 mg/L CaCO₃ are preferred.
📊 Comparison of Limits & Recommendations
| Παράμετρος | ΕΕ (Οδηγία 2020/2184) | WHO (ΠΟΥ) | ΗΠΑ (EPA, US) |
| TDS (Total Dissolved Solids) | ❌ Δεν υπάρχει ανώτατο όριο | <300 mg/L → Εξαιρετικό 300–600 mg/L → Καλό 600–900 mg/L → Αποδεκτό 900–1200 mg/L → Φτωχό >1200 mg/L → Ακατάλληλο |
500 mg/L → Secondary Maximum Contaminant Level (SMCL, αισθητικό όριο) |
| Σκληρότητα (ως CaCO₃) | ❌ Δεν υπάρχει όριο (μόνο ενδεικτικά για αισθητικά/τεχνικά ζητήματα) | Δεν υπάρχει υγειονομικό όριο. Συνιστάται ~80–500 mg/L για καλή ισορροπία γεύσης. |
Δεν υπάρχει υγειονομικό όριο. |
✅ Summary
- EU: It does not set specific limits for TDS or hardness, only for individual salts (e.g. nitrates, chlorine, lead).
- WHO: Uses TDS as a taste indicator.
- EPA (ΗΠΑ): Ορίζει 500 mg/L TDS ως δευτερεύον αισθητικό όριο.
👉 So, if we are talking purely about drinking water quality, a TDS of up to 500–600 mg/L is generally considered good tasting internationally.
Basic sources of the above are:
- European Directive 2020/2184/EU – on the quality of drinking water and general guidelines without strictly defined limits for TDS or hardness. Source: European Commission
- World Health Organization (WHO) – for the water quality guidelines and recommendations for TDS and other parameters. Source: WHO
- Environmental Protection Agency (EPA) – for the limits and recommendations of the USA regarding drinking water quality. Source: EPA
