WHO Potable Water Standard
The World Health Organization does not enforce strict "standards." Instead, it publishes Guidelines for Drinking-water Quality (GDWQ), which serve as a global benchmark for national standards.
1. Microbiological Parameters
- E. coli or Thermotolerant Coliforms: Zero (0) per 100 mL sample.
- Total Coliforms: Zero (0) per 100 mL sample in treated piped water supplies.
2. Chemical Parameters
| Parameter | WHO Guideline Value (Max Limit) | Primary Health Basis |
|---|---|---|
| Arsenic (As) | 0.01 mg/L (10 µg/L) | Carcinogen / Chronic toxicity |
| Lead (Pb) | 0.01 mg/L (10 µg/L) | Neurotoxin |
| Nitrate (as NO₃⁻) | 50.0 mg/L | Infant methemoglobinemia |
| Fluoride (F⁻) | 1.5 mg/L | Dental & skeletal fluorosis if exceeded |
| Chromium (Total) | 0.05 mg/L | Protection against chromium risks |
| Cadmium (Cd) | 0.003 mg/L | Kidney damage |
| Mercury (Total) | 0.006 mg/L | Central nervous system effects |
| Copper (Cu) | 2.0 mg/L | Gastrointestinal irritation |
3. Physical & Aesthetic Parameters
- pH Range: 6.5 to 8.5 is recommended for effective chlorination and to prevent pipe corrosion.
- Total Dissolved Solids: Water becomes increasingly unpalatable above 600 mg/L; no explicit health limit is set.
- Turbidity: Ideally < 1 NTU for effective disinfection.
- Taste, Odour, Appearance: Must be acceptable to consumers.
4. Disinfectants and Byproducts
- Free Residual Chlorine: Minimum 0.2 to 0.5 mg/L throughout the distribution network.
- Maximum Chlorine Limit: 5.0 mg/L.