 |
Chemical Quality Guidelines for Drinking Water |
Any drinking water always has chemicals present in it. There are three categories of chemicals that could be present in drinking water:
|
1. Chemicals of health significance in drinking-water: |
 | Inorganic constituents |
| Organic constituents |
| Pesticides |
| Disinfectants and disinfectant by-products |
| Radioactive constituents |
The guideline values for potentially hazardous chemicals are based on the tolerable daily intake (TDI), that is an estimate of the amount of a substance in food or drinking-water, expressed on a body weight basis (mg/kg or µg/kg of body weight), that can be ingested daily over a lifetime without appreciable health risk. Exposure by inhalation and dermal absorption of contaminants present in drinking water. The portion of the total tolerable daily intake (TDI) allocated to drinking water is generally sufficient to allow for additional routes of intake, as inhalation and dermal absorption of contaminants present in drinking water.
For setting the guideline values for potentially hazardous chemicals, a daily per capita consumption of 2 litres by a person weighing 60 kg was generally assumed. The guideline values set for drinking water using this assumption do, on average, err on the side of caution. However, such an assumption may underestimate the consumption of water per unit weight, and thus exposure, for those living in hot climates as well as for infants and children, who consume more fluid per unit weight than adults.
Short-term exposure to levels exceeding the TDI (as usual for travellers) is not a cause for concern, provided the individual's intake averaged over longer periods of time does not appreciably exceed the level set. The large safety factors generally used in establishing a TDI serve to provide assurance that exposure exceeding the TDI for short periods is unlikely to have any deleterious effects upon health. However, consideration should be given to any potential acute toxic effects that may occur if the TDI is substantially exceeded for short periods of time.
The World Health Organisation drinking-water quality guideline values are internationally accepted. For most contaminants, however, there is great scientific uncertainty, and a large uncertainty factor was used for setting them. Hence, there may be a large margin of safety above the guideline value before adverse health effects result.
In the following tables the World Health Organisation drinking-water quality guideline values are shown.
|
Inorganic Constituents |
| Guideline value (mg/litre) | Remarks | |
| antimony | 0.005 (P)a | |
| arsenic | 0.01b (P) | For excess skin cancer risk of 6 × 10-4 |
| barium | 0.7 | |
| beryllium | NADc (see References) | |
| boron | 0.5 (P) | |
| cadmium | 0.003 | |
| chromium | 0.05 (P) | |
| copper | 2 (P) | Based on acute gastrointestinal effects |
| cyanide | 0.07 | |
| fluoride | 1.5 | Climatic conditions, volume of water consumed, and intake from other sources should be considered when setting national standards |
| lead | 0.01 | It is recognised that not all water will meet the guideline value immediately; meanwhile, all other recommended measures to reduce the total exposure to lead should be implemented |
| manganese | 0.5 (P) | ATOd |
| mercury (total) | 0.001 | |
| molybdenum | 0.07 | |
| nickel | 0.02 (P) | |
| nitrate (as NO3-) | 50 (acute) | |
| nitrite (as NO2-) | 3 (acute) 0.2 (P) (chronic) | |
| selenium | 0.01 | |
| uranium | 0.002 (P) |
|
Organic Constituens |
| Guideline value (µg/litre) | Remarks | |
| Chlorinated alkanes | ||
| carbon tetrachloride | 2 | |
| dichloromethane | 20 | |
| 1,1-dichloroethane | ||
| 1,2-dichloroethane | 30b | NAD (see References) |
| 1,1,1-trichloroethane | 2000 (P) | For excess risk of 10-5 |
| Chlorinated ethenes | ||
| vinyl chloride | 5b | For excess risk of 10-5 |
| 1,1-dichloroethene | 30 | |
| 1,2-dichloroethene | 50 | |
| trichloroethene | 70 (P) | |
| tetrachloroethene | 40 | |
| Aromatic hydrocarbons | ||
| benzene | 10b | For excess risk of 10-5 |
| toluene | 700 | ATO |
| xylenes | 500 | ATO |
| ethylbenzene | 300 | ATO |
| styrene | 20 | ATO |
| benzo[a]pyrene | 0.7b | For excess risk of 10-5 |
| Chlorinated benzenes | ||
| monochlorobenzene | 300 | ATO |
| 1,2-dichlorobenzene | 1000 | ATO |
| 1,3-dichlorobenzene | NAD | |
| 1,4-dichlorobenzene | 300 | ATO |
| trichlorobenzenes (total) | 20 | ATO |
| Miscellaneous | ||
| di(2-ethylhexyl)adipate | 80 | |
| di(2-ethylhexyl)phthalate | 8 | |
| acrylamide | 0.5b | For excess risk of 10-5 |
| epichlorohydrin | 0.4 (P) | |
| hexachlorobutadiene | 0.6 | |
| edetic acid (EDTA) | 600 | |
| nitrilotriacetic acid | 200 | |
| dialkyltins | NAD | |
| tributyltin oxide | 2 | |
| microcystin-LR | 1 (P) | Applies to total microcystin-LR (free plus cell-bound) |
|
Pesticides |
|
Guideline value (µg/litre) |
Remarks |
|
| alachlor | 20b | For excess risk of 10-5 |
| aldicarb | 10 | |
| aldrin/dieldrin | 0.03 | |
| atrazine | 2 | |
| bentazone | 300 | |
| carbofuran | 7 | |
| chlordane | 0.2 | |
| chlorotoluron | 30 | |
| cyanazine | 0.6 | |
| DDT | 2 | |
| 1,2-dibromo-3-chloropropane | 1b | For excess risk of 10-5 |
| 1,2-dibromoethane | 0.4–15b (P) | For excess risk of 10-5 |
| 2,4-dichlorophenoxyacetic acid (2,4-D) | 30 | |
| 1,2-dichloropropane (1,2-DCP) | 40 (P) | |
| 1,3-dichloropropane | NAD | |
| 1,3-dichloropropene | 20b | For excess risk of 10-5 |
| diquat | 10 (P) | |
| heptachlor and heptachlor epoxide | 0.03 | |
| hexachlorobenzene | 1b | For excess risk of 10-5 |
| isoproturon | 9 | |
| lindane | 2 | |
| MCP | 2 | |
| methoxychlor | 20 | |
| metolachlor | 10 | |
| molinate | 6 | |
| pendimethalin | 20 | |
| pentachlorophenol | 9b (P) | For excess risk of 10-5 |
| permethrin | 20 | |
| propanil | 20 | |
| pyridate | 100 | |
| simazine | 2 | |
| terbuthylazine (TBA) | 7 | |
| trifluralin | 20 | |
| Chlorophenoxy herbicides other than 2,4-D and CPA | ||
| 2,4-DB | 90 | |
| dichlorprop | 100 | |
| fenoprop | 9 | |
| MCPB | NAD | |
| mecoprop | 10 | |
| 2,4,5-T | 9 | |
|
Disinfectants and disinfectant by-products |
|
Guideline value (mg/litre) |
Remarks | |
| monochloramine | 3 | |
| di- and trichloramine | NAD (see References) | |
| chlorine | 5 | ATO. For effective disinfection there should be a residual concentration of free chlorine of =0.5 mg/litre after at least 30 minutes contact time at pH <8.0 |
| chlorine dioxide | A guideline value has not been established because of the rapid breakdown of chlorine dioxide and because the chlorite guideline value is adequately protective for potential toxicity from chlorine dioxide | |
| iodine | NAD | |
| Disinfectant by-products | Guideline value (µg/litre) | Remarks |
| bromate | 25b (P) | For 7 × 10-5 excess risk |
| chlorate | NAD | |
| chlorite | 200 (P) | |
| Chlorophenols | ||
| 2-chlorophenol | NAD | |
| 2,4-dichlorophenol | NAD | |
| 2,4,6-trichlorophenol | 200 | For excess risk of 10-5, ATO |
| formaldehyde | 900 | |
| MX | NAD | |
| trihalomethanes | The sum of the ratio of the concentration of each to its respective guideline value should not exceed 1 | |
| bromoform | 100 | |
| dibromochloromethane | 100 | |
| bromodichloromethane | 60b | For excess risk of 10-5 |
| chloroform | 200 | |
| Chlorinated acetic acids | ||
| monochloroacetic acid | NAD | |
| dichloroacetic acid | 50 (P) | |
| trichloroacetic acid | 100 (P) | |
| chloral hydrate (trichloroacetaldehyde) | 10 (P) | |
| chloroacetone | NAD | |
| Halogenated acetonitriles | ||
| dichloroacetonitrile | 90 (P) | |
| dibromoacetonitrile | 100 (P) | |
| bromochloroacetonitrile | NAD | |
| trichloroacetonitrile | 1 (P) | |
| cyanogen chloride (as CN) | 70 | |
| chloropicrin | NAD | |
|
Radioactive constituents |
| Screening value (Bq/litre) | Remarks | |
| Gross alpha activity | 0,1 | |
| Gross alpha activity | 1 |
| a (P) - Provisional guideline value. This term is used for constituents for which there is some evidence of a potential hazard but where the available information on health effects is limited; or where an uncertainty factor greater than 1000 has been used in the derivation of the tolerable daily intake (TDI). Provisional guideline values are also recommended: (1) for substances for which the calculated guideline value would be below the practical quantification level, or below the level that can be achieved through practical treatment methods; or (2) where disinfection is likely to result in the guideline value being exceeded. |
| b For substances that are considered to be carcinogenic, the guideline value is the concentration in drinking-water associated with an excess lifetime cancer risk of
10-5 (one additional cancer per 100 000 of the population ingesting drinking-water containing the substance at the guideline value for 70 years). Concentrations associated with estimated excess lifetime cancer risks of
10-4 and 10-6 can be calculated by multiplying and dividing, respectively, the guideline value by 10. In cases in which the concentration associated with an excess lifetime cancer risk of 10-5 is not feasible as a result of inadequate analytical or treatment technology, a provisional guideline value is recommended at a practicable level and the estimated associated excess lifetime cancer risk presented. It should be emphasised that the guideline values for carcinogenic substances have been computed from hypothetical mathematical models that cannot be verified experimentally and that the values should be interpreted differently from TDI-based values because of the lack of precision of the models. At best, these values must be regarded as rough estimates of cancer risk. However, the models used are conservative and probably err on the side of caution. Moderate short-term exposure to levels exceeding the guideline value for carcinogens does not significantly affect the risk. |
| c NAD - No adequate data to permit recommendation of a health-based guideline value. |
| d ATO - Concentrations of the substance at or below the health-based guideline value may affect the appearance, taste, or odour of the water |
Back to: Inorganic constituents
- Organic constituents - Pesticides - Disinfectants and disinfectant by-products
- Radioactive constituents
|
2. Substances and parameters in drinking water that may give rise to complaints from consumers: |
|
Levels likely to give rise to consumer complaintsa |
Reasons for consumer complaints |
|
| Physical parameters | ||
| colour | 15 TCUb | appearance |
| taste and odour | - | should be acceptable |
| temperature | - | should be acceptable |
| turbidity | 5 NTUc | appearance; for effective terminal disinfection, median turbidity =1 NTU, single sample =5 NTU |
| Inorganic constituents | ||
| aluminium | 0.2 mg/l | depositions, discoloration |
| ammonia | 1.5 mg/l | odour and taste |
| chloride | 250 mg/l | taste, corrosion |
| copper | 1 mg/l | staining of laundry and sanitary ware (health-based provisional guideline value 2 mg/litre) |
| hardness | high hardness: scale deposition, scum formationlow hardness: possible corrosion | |
| hydrogen sulphide | 0.05 mg/l | odour and taste |
| iron | 0.3 mg/l | staining of laundry and sanitary ware |
| manganese | 0.1 mg/l | staining of laundry and sanitary ware (health-based guideline value 0.5 mg/litre) |
| dissolved oxygen | indirect effects | |
| pH | low pH: corrosion high pH: taste, soapy feelpreferably <8.0 for effective disinfection with chlorine | |
| sodium | 200 mg/l | taste |
| sulfate | 250 mg/l | taste, corrosion |
| total dissolved solids | 1000 mg/l | taste |
| zinc | 3 mg/l | appearance, taste |
| Organic constituents | ||
| toluene | 24-170 µg/l | odour, taste (health-based guideline value 700 µg/l) |
| xylene | 20-1800 µg/l | odour, taste (health-based guideline value 500 µg/l) |
| ethylbenzene | 2-200 µg/l | odour, taste (health-based guideline value 300 µg/l) |
| styrene | 4-2600 µg/l | odour, taste (health-based guideline value 20 µg/l) |
| monochlorobenzene | 10-120 µg/l | odour, taste (health-based guideline value 300 µg/l) |
| 1,2-dichlorobenzene | 1-10 µg/l | odour, taste (health-based guideline value 1000 µg/l) |
| 1,4-dichlorobenzene | 0.3-30 µg/l | odour, taste (health-based guideline value 300 µg/l) |
| trichlorobenzenes (total) | 5-50 µg/l | odour, taste (health-based guideline value 20 µg/l) |
| synthetic detergents | foaming, taste, odour | |
| Disinfectants and disinfectant by-products | ||
| chlorine | 600-1000 µg/l | taste and odour (health-based guideline value 5 µg/l) |
| chlorophenols | ||
| 2-chlorophenol | 0.1-10 µg/l | taste, odour |
| 2,4-dichlorophenol | 0.3-40 µg/l | taste, odour |
| 2,4,6-trichlorophenol | 2-300 µg/l | taste, odour (health-based guideline value 200 µg/l) |
a The levels indicated are not precise numbers. Problems may occur at lower or higher values according to local circumstances. A range of taste and odour threshold concentrations is given for organic constituents.
b TCU, true colour unit.
c NTU, nephelometric turbidity unit.
|
3. Chemicals not of health significance at concentrations normally found in drinking-water: |
U - It is unnecessary to recommend a health-based guideline value for these compounds because they are not hazardous to human health at concentrations normally found in drinking water.