The World Health Organization (WHO) has established Guidelines for drinking-water quality covering microbial, chemical, radiological and acceptability hazards. These are health-based international recommendations that countries use to develop their own legally enforceable standards.
This is HL-only content in IB ESS subtopic 4.4 Water pollution. WHO’s approach is not limited to testing the final water supply: it promotes risk management from the water catchment to the consumer through health-based targets, water safety plans and independent surveillance.
| Guideline area | What WHO assesses | Key example |
|---|---|---|
| Microbial quality | Pathogens and evidence of faecal contamination | E. coli must not be detectable in any 100 mL sample of water intended for drinking. |
| Chemical quality | Naturally occurring and human-made contaminants that may cause acute or long-term harm | Guideline values include arsenic at 0.01 mg/L, fluoride at 1.5 mg/L and nitrate at 50 mg/L. |
| Radiological quality | Exposure to radionuclides in drinking water | Screening values and guidance levels indicate when further investigation is required. |
| Acceptability | Taste, odour and appearance | Water should be acceptable to consumers; otherwise, they may use less safe alternatives. |
Chemical guideline values generally represent concentrations that do not create an intolerable health risk over a lifetime of consumption. However, values may also protect vulnerable groups, such as infants exposed to nitrate.
A common misconception is that WHO guidelines are universal laws. They are recommendations: national or local governments adapt them according to environmental conditions, exposure, treatment technology and socioeconomic capacity, then may establish statutory standards. For example, WHO’s arsenic guideline provides a benchmark for managing groundwater contamination in Bangladesh, but achieving it depends on monitoring, infrastructure and equitable access to safe alternatives.
Exam technique: For an “explain” question, distinguish WHO guidance from national law and connect guideline values to monitoring and management. For an “evaluate” question, consider public-health protection, feasibility, cost and environmental justice rather than merely listing limits.