Comprehensive WHO water safety framework for public health authorities, water suppliers, and surveillance agencies worldwide.
What this guideline saysGMJ summary
The WHO Guidelines for drinking-water quality provide the global reference for safe drinking-water management through a preventive risk-based framework. The fourth edition, incorporating three addenda (latest updates through 2026), establishes health-based targets, water safety plans (WSPs), and independent surveillance as the three pillars of ensuring water safety from catchment to consumer.
The Guidelines prioritize microbial safety as the paramount concern, while providing guideline values for chemical and radiological contaminants based on tolerable disease burden of 10⁻⁶ DALY per person per year. Key chemical priorities include arsenic, fluoride, lead, nitrate, manganese, and selenium where exposures can cause widespread health effects. The framework emphasizes multiple barriers, system assessment, operational monitoring, and verification rather than end-product testing alone.
Recent updates include revised guidance on manganese (new guideline value 0.08 mg/L considering health significance), chromium, nickel, cyanobacterial toxins, radon management, climate resilience, wastewater reuse, and vector control pesticides. The approach is adaptable to all supply types from large utilities to small community-managed systems and household treatment.
Key pointsfor clinicians
- Escherichia coli must not be detectable in any 100 mL sample of treated drinking-water entering or within the distribution system; presence indicates recent faecal contamination requiring immediate investigation and corrective action
- Tolerable disease burden set at 10⁻⁶ DALY per person per year as basis for all health-based targets; approximately equivalent to 10⁻⁵ excess lifetime cancer risk (1 case per 100,000 over 70 years)
- Priority chemical contaminants with widespread health impacts: arsenic (GV 0.01 mg/L), fluoride (GV 1.5 mg/L, adjust for climate and consumption), lead (GV 0.01 mg/L), nitrate (GV 50 mg/L as NO₃⁻), manganese (GV 0.08 mg/L)
- Disinfection must never be compromised to control disinfection by-products; effective pathogen inactivation is paramount with DBP risks orders of magnitude lower than inadequate disinfection risks
- Minimum water service levels: ≥20 L per person per day from source <1000 m away or collection time <30 minutes total, with reliable daily access and affordability <3% household income
- Radiological screening: gross alpha activity >0.5 Bq/L or gross beta >1 Bq/L triggers investigation of specific radionuclides; radon reference level 100 Bq/L
- Water safety plans required with five components: (1) multidisciplinary team preparation, (2) system assessment identifying hazards/risks, (3) operational monitoring of control measures, (4) management procedures and communication, (5) regular review and improvement
- Treatment performance targets for reference pathogens: typically 4-log (99.99%) reduction for viruses, 3-log for protozoa (Cryptosporidium), 2-log for bacteria from surface waters; validated treatment processes required
Minimum water quantities for basic health needs and service levelsextracted from the guideline
| Service level | Access measure | Level of health concern | Needs met |
|---|---|---|---|
| No access (quantity collected <5 L per capita per day) | More than 1000 m or 30 min total collection time | Very high | Consumption – cannot be assured; Hygiene – not possible (unless practised at source) |
| Basic access (average quantity unlikely to exceed 20 L per capita per day) | Between 100 and 1000 m or 5 to 30 min total collection time | High | Consumption – should be assured; Hygiene – handwashing and basic food hygiene possible; laundry/bathing difficult to assure unless carried out at source |
| Intermediate access (average quantity ~50 L per capita per day) | Water delivered through one tap on plot or within 100 m or 5 min total collection time | Low | Consumption – assured; Hygiene – all basic personal and food hygiene assured; laundry and bathing should be assured |
| Optimal access (average quantity >100 L per capita per day) | Water supplied through multiple taps continuously | Very low | Consumption – all needs met; Hygiene – all needs should be met |
What changed in this edition
- 2026 third addendum: Updated microbial pathogen information including priority waterborne pathogens, new/updated fact sheets for bacterial, viral, protozoan and helminth pathogens
- 2026: Enhanced WSP guidance emphasizing government role, sanitary inspection integration, updated risk prioritization matrices based on WSP audit/sanitary inspection scores
- 2026: Revised pesticide guidance for vector control in drinking-water reflecting latest WHO prequalification programme, deletion of individual pesticide fact sheets
- 2022 second addendum: New guideline value for manganese (0.08 mg/L health-based, 0.1 mg/L aesthetic), updated chromium (0.05 mg/L total chromium), nickel (0.07 mg/L)
- 2022: Updated cyanotoxin guidance including alert level frameworks for anatoxins, cylindrospermopsins, microcystins, saxitoxins
- 2022: Revised radiological guidance for screening values and radon management (reference level 100 Bq/L)
- 2022: New reference values concept introduced for certain chemicals where health-based values are below analytical achievability or treatment capacity
- 2022: Enhanced climate change considerations, new wastewater reuse section, updated emergency response and food production guidance
- 2017 first addendum: Updated guideline values for barium (1.3 mg/L), bentazone (removed due to low toxicity), chlorine dioxide/chlorate/chlorite, perchlorate (0.07 mg/L), nitrate/nitrite, MCPA, diquat, dicofol, dichlorvos
ApplicabilityGeorgia and the region
For Georgia and the South Caucasus, these Guidelines provide the authoritative framework for developing national drinking-water standards and surveillance programmes. Key regional priorities include: arsenic in groundwater (particularly in agricultural areas), seasonal microbial contamination during spring floods and heavy rainfall, ageing Soviet-era distribution infrastructure with cross-connection risks, small rural community supplies often lacking treatment, and growing urban water stress. National programmes should conduct drinking-water quality assessments to identify whether fluoride, nitrate from fertilizer use, or metals from mining activities require specific attention. The WSP approach is directly applicable to municipal utilities in Tbilisi, Yerevan and Baku, while the small water supplies guidance and sanitary inspection tools are critical for rural areas where community-managed springs, wells and non-piped supplies predominate. Climate change impacts—increasing drought periods affecting source water availability and quality, plus intense rainfall overwhelming treatment—require integration into water safety planning. Health authorities should prioritize microbial safety through chlorination and source protection, establish E. coli monitoring programmes, and develop context-specific chemical standards based on local exposure data rather than adopting all guideline values uniformly.
Questions this guideline answers
What is the single most important drinking-water quality parameter to monitor?
Escherichia coli as indicator of faecal contamination. It must not be detectable in treated water. Microbial contamination is the greatest and most widespread health risk, while E. coli testing is feasible even in low-resource settings. However, E. coli monitoring must be combined with sanitary inspection or WSP assessment, not relied upon alone, as water quality can change rapidly between tests.
How do I know which of the 100+ chemicals with guideline values to test for in my water supply?
Conduct a drinking-water quality assessment considering: catchment activities (agriculture, industry, mining, wastewater), geology (arsenic, fluoride, uranium), treatment chemicals used, and distribution system materials (lead pipes, cement linings). Globally, only arsenic, fluoride, nitrate, lead, manganese, selenium and uranium have caused widespread health effects through drinking-water. Focus monitoring resources on chemicals known or likely to be present at significant levels, not on comprehensive testing of all parameters. The Guidelines explicitly state that testing everything is neither feasible nor good use of scarce resources.
What is the minimum treatment required for surface water used for drinking?
Surface water requires both effective disinfection and prior treatment to reduce turbidity and remove particles that protect pathogens from disinfection. Typical performance targets are ≥4-log virus reduction, ≥3-log Cryptosporidium reduction, ≥2-log bacteria reduction through multiple barriers (e.g., coagulation-filtration plus chlorination). Disinfection alone without particle removal is insufficient for surface water. Turbidity should be <1 NTU for effective disinfection, ideally <0.1 NTU after filtration. Chlorine residual of 0.5 mg/L after 30 min contact time at pH <8 typically achieves bacterial/viral inactivation but not Cryptosporidium.
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Other guidelines on this topic
- Issuer
- World Health Organization
- Type
- Guideline
- Edition
- 4th edition, 2026 (incorporating 1st, 2nd and 3rd addenda)
- Replaces
- Guidelines for drinking-water quality, 4th edition incorporating 1st and 2nd addenda, 2022
- Status
- Current
- Published
- 2026-06-08
- Languages
- English (translations available in multiple languages via WHO regional offices)
- Scope
- All drinking-water supplies: large piped municipal systems, small community supplies, non-piped supplies, household treatment, packaged water, specific settings (buildings, health-care facilities, aircraft, ships, emergencies)
- Audience
- Water and health regulators, policy-makers, public health authorities, water suppliers, surveillance agencies, local governments, community water managers, water safety professionals
- Pages
- 647
- Licence
- CC BY-NC-SA 3.0 IGO
- ISBN
- 978-92-4-012122-5
- Evidence
- Systematic review of peer-reviewed toxicological and epidemiological evidence for chemical guideline values; quantitative microbial risk assessment for pathogens; expert consensus through Guideline Development Group and technical working groups; international chemical risk assessments (JECFA, JMPR, IPCS)
- Next review
- Continuous rolling revision process; 5th edition in development; chemical and microbial fact sheets updated as new evidence emerges
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