WHO Guidelines for Drinking Water Quality: A Global Standard
An in-depth look at the World Health Organization (WHO) guidelines for drinking water. Understand the key parameters for safe water and how they influence global health standards.
The World Health Organization (WHO) Guidelines for Drinking-water Quality (GDWQ) are the international benchmark for drinking water safety. They provide the scientific basis for national regulations and standards worldwide, ensuring that water consumed by populations is free from pathogens and toxic chemicals.
Unlike rigid "standards," the WHO provides "guidelines." This means they offer a framework that countries can adapt based on their own local environmental, social, and economic conditions.
Key Principles of Water Safety
The WHO emphasizes a holistic approach known as a Water Safety Plan (WSP). Instead of just testing the final water, a WSP requires:
- System Assessment: Understanding the entire water supply chain from catchment to consumer.
- Monitoring: Checking control measures at specific points (e.g., filtration, disinfection).
- Management: Having plans in place for normal operation and incidents.
Microbiological Guidelines (The Most Critical)
The WHO states that the most common and widespread health risk associated with drinking water is microbial contamination.
| Parameter | Guideline Value |
|---|---|
| E. coli | Must not be detectable in any 100 ml sample |
| Thermotolerant Coliforms | Must not be detectable in any 100 ml sample |
| Viruses / Protozoa | No specific numeric guideline; requires effective treatment (filtration + disinfection) to meet health-based targets. |
Disinfection: For effective disinfection, the guidelines suggest a residual chlorine level of at least 0.5 mg/L after 30 minutes of contact time at pH < 8.0.
Chemical Guidelines (Selected Key Parameters)
Chemical constituents are generally a concern for long-term health exposure rather than acute illness.
| Chemical | Guideline Value (Max) | Health Concern |
|---|---|---|
| Arsenic | 0.01 mg/L (10 µg/L) | Cancer, skin lesions |
| Fluoride | 1.5 mg/L | Skeletal fluorosis |
| Lead | 0.01 mg/L (10 µg/L) | Neurological development (children) |
| Nitrate | 50 mg/L | Blue baby syndrome (Methaemoglobinaemia) |
| Mercury | 0.006 mg/L | Kidney damage |
| Copper | 2 mg/L | Gastrointestinal distress |
| Chlorine | 5 mg/L | (Effective disinfection requires much less) |
Physical/Aesthetic Parameters
While these do not directly impact health, they affect whether people will drink the water.
- TDS (Total Dissolved Solids): No health-based guideline, but water becomes unpalatable above 600–1000 mg/L.
- Turbidity: < 1 NTU is recommended for effective disinfection.
- Color/Odor: Should be acceptable to consumers.