Health Topics

Water

     WHO Water Drinking Guidelines

     The Role of Ministries of Health in reducing disease burden due to Water, Sanitation and Hygiene related illness

     Arsenic in Drinking Water and resulting Arsenic Toxicity in India and Bangladesh

     WHO Water Drinking Guidelines

WHO’s Guidelines for drinking water Quality are updated every few years. A three volume publication examines microbiological, biological, chemical and radiological aspects of drinking water. It evaluates 36 inorganic constituents, 27 industrial chemicals, 36 pesticides, four disinfectants and 23 disinfectant by-products.

     Bacteriological quality of drinking water ^a

     Chemicals of health significance in drinking water

     Inorganic Constituents

     Organic Constituents

     Pesticides

      Bacteriological quality of drinking water ^a

a.    Immediate investigative action must be taken if either E.coli or total coliform bacteria are detected. The minimum action in the case of total coliform bacteria is repeat sampling; if these bacteria are detected in the repeat sample, the cause must be determined by immediate further investigation.

b.    Although E.coli is the more precise indicator of faecal pollution, the count of thermotolerant coliform bacteria is an acceptable alternative. If necessary, proper confirmatory tests must be carried out. Total coliform bacteria are not acceptable indicators of the sanitary quality of rural water supplies, particularly in tropical areas where many bacteria of no sanitary significance occur in almost all untreated supplies.

c.     It is recognised that, in the great majority of rural water supplies in developing countries, faecal contamination is widespread. Under these conditions, the national surveillance agency should set medium-term targets for progressive improvement of water supplies, as recommended in Volume 3 of Guidelines for drinking-water quality.

     Chemicals of health significance in drinking water
 

     Inorganic Constituents

      Organic Constituents

     Pesticides

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 qualification level, 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 us the concentration in drinking water associated with an excess lifetime cancer risk of 10-5 (one additional cancer per 100000 of the population ingested 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 in adequate 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 experimental experimentally and that the values should be interpreted differently that the TDI- based values because of the lack if 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.