Introduction to WHO Guidelines
The World Health Organization (WHO)'s Guidelines for Drinking-water Quality, established in Geneva in 1993, serve as a foundational international reference for setting drinking water standards and ensuring water safety globally. These guidelines provide a comprehensive framework for assessing the quality of drinking water, outlining health-based limits for various substances, from common inorganic elements to complex organic compounds and disinfection by-products.
Understanding and adhering to these guidelines is crucial for public health protection and for guiding water treatment professionals in designing effective purification processes. This document outlines the key parameters and their respective guidelines as per the 1993 publication.
For a broader perspective on drinking water quality, you may also find our article on Drinking Water Standards insightful.
Inorganic Substances in Drinking Water
The presence of inorganic elements and compounds in drinking water can originate from natural geological formations, agricultural runoff, or industrial discharges. The WHO guidelines set health-based limits to mitigate potential risks.
| Element/Substance | Symbol/Formula | Normally Found in Freshwater (Concentration) | WHO Health-Based Guideline (Concentration) |
|---|
| Aluminium | Al | 0.2 mg/L (0.2 ppm) | No guideline |
| Ammonia | NH₄ | < 0.2 mg/L (up to 0.3 mg/L in anaerobic waters) | No guideline |
| Antimony | Sb | < 4 µg/L (4 ppb) | 0.005 mg/L (5 ppb) |
| Arsenic | As | 0.01 mg/L (10 ppb) | 0.01 mg/L (10 ppb) |
| Asbestos | | | No guideline |
| Barium | Ba | 0.3 mg/L (0.3 ppm) | 0.7 mg/L (0.7 ppm) |
| Beryllium | Be | < 1 µg/L (1 ppb) | No guideline |
| Boron | B | < 1 mg/L (1 ppm) | 0.3 mg/L (0.3 ppm) |
| Cadmium | Cd | < 1 µg/L (1 ppb) | 0.003 mg/L (3 ppb) |
| Chloride | Cl | 250 mg/L (250 ppm) | 250 mg/L (250 ppm) |
| Chromium | Cr³⁺, Cr⁶⁺ | < 2 µg/L (2 ppb) | 0.05 mg/L (50 ppb) |
| Colour | | Not mentioned | No guideline |
| Copper | Cu | 2 mg/L (2 ppm) | 2 mg/L (2 ppm) |
| Cyanide | CN⁻ | | 0.07 mg/L (70 ppb) |
| Dissolved oxygen | O₂ | | No guideline |
| Fluoride | F | < 1.5 mg/L (up to 10 mg/L) | 1.5 mg/L (1.5 ppm) |
| Hardness | mg/L CaCO₃ | | No guideline |
| Hydrogen sulfide | H₂S | | No guideline |
| Iron | Fe | 0.5 - 50 mg/L (0.5 - 50 ppm) | No guideline |
| Lead | Pb | | 0.01 mg/L (10 ppb) |
| Manganese | Mn | 0.5 mg/L (0.5 ppm) | 0.05 mg/L (50 ppb) |
| Mercury | Hg | < 0.5 µg/L (0.5 ppb) | 0.001 mg/L (1 ppb) |
| Molybdenum | Mo | < 0.01 mg/L (10 ppb) | 0.07 mg/L (70 ppb) |
| Nickel | Ni | < 0.02 mg/L (20 ppb) | 0.02 mg/L (20 ppb) |
| Nitrate and nitrite | NO₃, NO₂ | 50 mg/L total nitrogen (50 ppm) | 50 mg/L total nitrogen (50 ppm) |
| Turbidity | | Not mentioned | No guideline |
| pH | | | No guideline |
| Selenium | Se | < 0.01 mg/L (10 ppb) | 0.01 mg/L (10 ppb) |
| Silver | Ag | 5 – 50 µg/L (5 – 50 ppb) | No guideline |
| Sodium | Na | < 20 mg/L (20 ppm) | 200 mg/L (200 ppm) |
| Sulfate | SO₄ | 500 mg/L (500 ppm) | 500 mg/L (500 ppm) |
| Inorganic tin | Sn | | No guideline |
| TDS (Total Dissolved Solids) | | | No guideline |
| Uranium | U | | 1.4 mg/L (1.4 ppm) |
| Zinc | Zn | 3 mg/L (3 ppm) | 3 mg/L (3 ppm) |
Organic Compounds in Drinking Water
Organic compounds can enter drinking water sources from various anthropogenic activities, including industrial processes, agriculture, and urban runoff. The WHO guidelines provide limits for numerous organic contaminants.
Chlorinated Alkanes
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| Carbon tetrachloride | CCl₄ | 2 µg/L (2 ppb) |
| Dichloromethane | CH₂Cl₂ | 20 µg/L (20 ppb) |
| 1,1-Dichloroethane | C₂H₄Cl₂ | No guideline |
| 1,2-Dichloroethane | ClCH₂CH₂Cl | 30 µg/L (30 ppb) |
| 1,1,1-Trichloroethane | CH₃CCl₃ | 2000 µg/L (2000 ppb) |
Chlorinated Ethenes
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| 1,1-Dichloroethene | C₂H₂Cl₂ | 30 µg/L (30 ppb) |
| 1,2-Dichloroethene | C₂H₂Cl₂ | 50 µg/L (50 ppb) |
| Trichloroethene | C₂HCl₃ | 70 µg/L (70 ppb) |
| Tetrachloroethene | C₂Cl₄ | 40 µg/L (40 ppb) |
Aromatic Hydrocarbons
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| Benzene | C₆H₆ | 10 µg/L (10 ppb) |
| Toluene | C₇H₈ | 700 µg/L (700 ppb) |
| Xylenes | C₈H₁₀ | 500 µg/L (500 ppb) |
| Ethylbenzene | C₈H₁₀ | 300 µg/L (300 ppb) |
| Styrene | C₈H₈ | 20 µg/L (20 ppb) |
Polynuclear Aromatic Hydrocarbons (PAHs)
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| PAHs | C₂H₃N₁O₅P₁₃ (?) | 0.7 µg/L (0.7 ppb) |
Note: The formula provided for PAHs (C₂H₃N₁O₅P₁₃) is unusual as PAHs are typically hydrocarbons (only carbon and hydrogen). This guideline usually refers to a sum of specific PAHs.
Chlorinated Benzenes
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| Monochlorobenzene (MCB) | C₆H₅Cl | 300 µg/L (300 ppb) |
| 1,2-Dichlorobenzene (1,2-DCB) | C₆H₄Cl₂ | 1000 µg/L (1000 ppb) |
| 1,3-Dichlorobenzene (1,3-DCB) | C₆H₄Cl₂ | No guideline |
| 1,4-Dichlorobenzene (1,4-DCB) | C₆H₄Cl₂ | 300 µg/L (300 ppb) |
| Trichlorobenzenes (TCBs) | C₆H₃Cl₃ | 20 µg/L (20 ppb) |
Miscellaneous Organic Constituents
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| Di(2-ethylhexyl)adipate (DEHA) | C₂₂H₄₂O₄ | 80 µg/L (80 ppb) |
| Di(2-ethylhexyl)phthalate (DEHP) | C₂₄H₃₈O₄ | 8 µg/L (8 ppb) |
| Acrylamide | C₃H₅NO | 0.5 µg/L (0.5 ppb) |
| Epichlorohydrin (ECH) | C₃H₅ClO | 0.4 µg/L (0.4 ppb) |
| Hexachlorobutadiene (HCBD) | C₄Cl₆ | 0.6 µg/L (0.6 ppb) |
| Ethylenediaminetetraacetic acid (EDTA) | C₁₀H₁₂N₂O₈ | 200 µg/L (200 ppb) |
| Nitrilotriacetic acid (NTA) | N(CH₂COOH)₃ | 200 µg/L (200 ppb) |
Organotins
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| Dialkyltins | R₂SnX₂ | No guideline |
| Tributyltin oxide (TBTO) | C₂₄H₅₄OSn₂ | 2 µg/L (2 ppb) |
Pesticides in Drinking Water
Pesticides are widely used in agriculture and can contaminate water sources through runoff and leaching. The WHO sets guidelines for various pesticides due to their potential health impacts.
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| Alachlor | C₁₄H₂₀ClNO₂ | 20 µg/L (20 ppb) |
| Aldicarb | C₇H₁₄N₂O₄S | 10 µg/L (10 ppb) |
| Aldrin and dieldrin | C₁₂H₈Cl₆ / C₁₂H₈Cl₆O | 0.03 µg/L (0.03 ppb) |
| Atrazine | C₈H₁₄ClN₅ | 2 µg/L (2 ppb) |
| Bentazone | C₁₀H₁₂N₂O₃S | 30 µg/L (30 ppb) |
| Carbofuran | C₁₂H₁₅NO₃ | 5 µg/L (5 ppb) |
| Chlordane | C₁₀H₆Cl₈ | 0.2 µg/L (0.2 ppb) |
| Chlorotoluron | C₁₀H₁₃ClN₂O | 30 µg/L (30 ppb) |
| DDT | C₁₄H₉Cl₅ | 2 µg/L (2 ppb) |
| 1,2-Dibromo-3-chloropropane | C₃H₅Br₂Cl | 1 µg/L (1 ppb) |
| 2,4-Dichlorophenoxyacetic acid (2,4-D) | C₈H₆Cl₂O₃ | 30 µg/L (30 ppb) |
| 1,2-Dichloropropane | C₃H₆Cl₂ | No guideline |
| 1,3-Dichloropropane | C₃H₆Cl₂ | 20 µg/L (20 ppb) |
| 1,3-Dichloropropene | CH₃CHClCH₂Cl | No guideline |
| Ethylene dibromide (EDB) | BrCH₂CH₂Br | No guideline |
| Heptachlor and heptachlor epoxide | C₁₀H₅Cl₇ / C₁₀H₅Cl₇O | 0.03 µg/L (0.03 ppb) |
| Hexachlorobenzene (HCB) | C₁₀H₅Cl₇O | 1 µg/L (1 ppb) |
| Isoproturon | C₁₂H₁₈N₂O | 9 µg/L (9 ppb) |
| Lindane | C₆H₆Cl₆ | 2 µg/L (2 ppb) |
| MCPA | C₉H₉ClO₃ | 2 µg/L (2 ppb) |
| Methoxychlor | (C₆H₄OCH₃)₂CHCCl₃ | 20 µg/L (20 ppb) |
| Metolachlor | C₁₅H₂₂ClNO₂ | 10 µg/L (10 ppb) |
| Molinate | C₉H₁₇NOS | 6 µg/L (6 ppb) |
| Pendimethalin | C₁₃H₁₉O₄N₃ | 20 µg/L (20 ppb) |
| Pentachlorophenol (PCP) | C₆HCl₅O | 9 µg/L (9 ppb) |
| Permethrin | C₂₁H₂₀Cl₂O₃ | 20 µg/L (20 ppb) |
| Propanil | C₉H₉Cl₂NO | 20 µg/L (20 ppb) |
| Pyridate | C₁₉H₂₃ClN₂O₂S | 100 µg/L (100 ppb) |
| Simazine | C₇H₁₂ClN₅ | 2 µg/L (2 ppb) |
| Trifluralin | C₁₃H₁₆F₃N₃O₄ | 20 µg/L (20 ppb) |
Chlorophenoxy Herbicides (excluding 2,4-D and MCPA)
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| 2,4-DB | C₁₀H₁₀Cl₂O₃ | 90 µg/L (90 ppb) |
| Dichlorprop | C₉H₈Cl₂O₃ | 100 µg/L (100 ppb) |
| Fenoprop | C₉H₇Cl₃O₃ | 9 µg/L (9 ppb) |
| MCPB | C₁₁H₁₃ClO₃ | No guideline |
| Mecoprop | C₁₀H₁₁ClO₃ | 10 µg/L (10 ppb) |
| 2,4,5-T | C₈H₅Cl₃O₃ | 9 µg/L (9 ppb) |
Disinfectants and Disinfection By-products
Disinfectants are essential for treating drinking water, but they can react with natural organic matter to form disinfection by-products (DBPs), some of which may be harmful.
Disinfectants
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| Chloramines | NHₙCl(₃₋ₙ), where n = 0, 1 or 2 | 3 mg/L (3 ppm) |
| Chlorine | Cl₂ | 5 mg/L (5 ppm) |
| Chlorine dioxide | ClO₂ | No guideline |
| Iodine | I₂ | No guideline |
Disinfectant By-products
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| Bromate | BrO₃⁻ | 25 µg/L (25 ppb) |
| Chlorate | ClO₃⁻ | No guideline |
| Chlorite | ClO₂⁻ | 200 µg/L (200 ppb) |
| Formaldehyde | HCHO | 900 µg/L (900 ppb) |
| MX (3-Chloro-4-dichloromethyl-5-hydroxy-2(5H)-furanone) | C₅H₃Cl₃O₃ | No guideline |
| Cyanogen chloride | ClCN | 70 µg/L (70 ppb) |
| Chloropicrin | CCl₃NO₂ | No guideline |
Chlorophenols
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| 2-Chlorophenol (2-CP) | C₆H₅ClO | No guideline |
| 2,4-Dichlorophenol (2,4-DCP) | C₆H₄Cl₂O | No guideline |
| 2,4,6-Trichlorophenol (2,4,6-TCP) | C₆H₃Cl₃O | 200 µg/L (200 ppb) |
Trihalomethanes
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| Bromoform | CHBr₃ | 100 µg/L (100 ppb) |
| Dibromochloromethane | CHBr₂Cl | 100 µg/L (100 ppb) |
| Bromodichloromethane | CHBrCl₂ | 60 µg/L (60 ppb) |
| Chloroform | CHCl₃ | 200 µg/L (200 ppb) |
Chlorinated Acetic Acids
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| Monochloroacetic acid | C₂H₃ClO₂ | No guideline |
| Dichloroacetic acid | C₂H₂Cl₂O₂ | 50 µg/L (50 ppb) |
| Trichloroacetic acid | C₂HCl₃O₂ | 100 µg/L (100 ppb) |
| Chloral hydrate (trichloroacetaldehyde) | CCl₃CH(OH)₂ | 10 µg/L (10 ppb) |
| Chloroacetones | C₃H₅OCl | No guideline |
Halogenated Acetonitriles
| Substance | Formula | WHO Health-Based Guideline (Concentration) |
|---|
| Dichloroacetonitrile | C₂HCl₂N | 90 µg/L (90 ppb) |
| Dibromoacetonitrile | C₂HBr₂N | 100 µg/L (100 ppb) |
| Bromochloroacetonitrile | CHCl₂CN | No guideline |
| Trichloroacetonitrile | C₂Cl₃N | 1 µg/L (1 ppb) |
AquaChain Engineering Tip
When monitoring for compliance with WHO guidelines, prioritize sampling strategies based on the vulnerability of your water source and the specific treatment processes in place. For instance, if chlorination is used, implement a robust DBP monitoring plan, especially for trihalomethanes and haloacetic acids, at various points in the distribution network to capture peak formation. Regular analytical checks using certified laboratories are non-negotiable for ensuring ongoing compliance and public safety.
Frequently Asked Questions
Q: What is the primary purpose of the WHO Drinking-Water Quality Guidelines?
A: The guidelines serve as an international reference to promote and protect public health by establishing a scientific basis for national drinking water quality standards and risk management strategies.
Q: Are these guidelines legally binding for all countries?
A: No, the WHO guidelines are not legally binding; they are recommendations that countries adapt into their national regulations based on local conditions, resources, and priorities.
Q: Why are there "No guideline" entries for some substances?
A: "No guideline" entries typically indicate that, at the time of publication, there was either insufficient toxicological data to set a health-based value, or the substance was not considered a significant health concern at typical environmental concentrations.