Water for people.pdf - WHO Thailand Digital Repository

1 0 6 / C H A L L E N G E S T O L I F E A N D W E L L - B E I N GBasic Needs and the Right to HealthTable 5.2: Six scenarios of exposure to environmental faecal-oral pathogensEnvironmental faecal-Scenario Description oral pathogen loadVI No improved water supply and no basic sanitation in a country that is not extensively covered by those services, Very highand where water supply is not routinely controlledVb Improved water supply and no basic sanitation in a country that is not extensively covered by those services, Very highand where water supply is not routinely controlledVa Basic sanitation but no improved water supply in a country that is not extensively covered by those services, Highand where water supply is not routinely controlledIV Improved water supply and basic sanitation in a country that is not extensively covered by those services, Highand where water supply is not routinely controlledIIIc IV and improved access to drinking water (generally piped to household) HighIIIb IV and improved personal hygiene HighIIIa IV and drinking water disinfected at point of use HighII Regulated water supply and full sanitation coverage, with partial treatment for sewage, corresponding to a Medium to lowsituation typically occurring in developed countriesI Ideal situation, corresponding to the absence of transmission of diarrhoeal diseases through water, sanitation Lowand hygieneThis figure shows how the risks of human contamination from faecal-oral diseases vary according to different levels of provision for water, sanitation and hygiene. An obvious link is to be observedbetween health gains and improved service levels.Source: Based on table 2 and figure 2 in Prüss et al., 2002, pp. 539–40.■ illustrates the high potential for disease reduction by simplemethods such as safe drinking water storage and disinfection atthe household level.The paucity of data from the field continues to be a constraint, asillustrated in the box on cholera earlier.WHO is currently embarking on analyses to clarify theattributable fraction of the burden of disease to ecosystemcomponents of water resource development projects, for malaria,schistosomiasis, filariasis and Japanese encephalitis.Chemical water quality parameters are partly responsible for theill-health related to drinking water supply. These chemicals include theinorganic compounds fluor, arsenic, cadmium and uranium which mayoccur naturally in aquifers used for drinking water withdrawals.Because of the arsenic crisis in Bangladesh (35 million people exposedthrough drinking water supply boreholes) attention has recently beenfocused on this compound, but it is estimated that the health impactof naturally occurring fluor is more widespread. The health conditionresulting from exposure to fluor over and above a certain threshold isknown as fluorosis and affects the skeletal tissues. The heavierelements cadmium and uranium cause kidney damage with resorptionof minerals from the bone as a secondary effect.Industrial waste and agricultural runoff are the major sources oforganic pollution, and the impact of exposure to these compoundsand their residues may be characterized as one or more of thefollowing: mutagenic, carcinogenic, teratogenic, toxic to the embryoor causing reproductive toxicity; details are provided in theGuidelines for Drinking Water Quality (WHO, 1996). Of growingconcern are the endocrine disrupting chemicals (EDCs), exposure towhich may modulate the endocrine system. While drinking water is apotential source of human exposure to EDCs, it is not considered amajor exposure pathway unless unusual contamination has occurred(WHO, 2002d).Vector-borne diseasesTwo characteristics distinguish the water-related vector-bornediseases from the water-borne diseases: their transmission mode andthe nature of their association with water. Insects, essentiallybloodsucking species, play a key role in the transmission of diseasessuch as malaria, filariasis and various infections of a viral etiology(e.g. yellow fever, West Nile virus, Japanese encephalitis anddengue). This role is not simply a mechanical one of takingpathogens from an infected to a not-infected person. Usually, thevector itself provides conditions required for the development of partof a parasite lifecycle. Aquatic and amphibious snails that serve asintermediate hosts for the Schistosoma parasites equally provide acrucial habitat for the development of their infective larvae, but theydo not actually play an active role in the transmission from oneperson to another. In the case of schistosomiasis (bilharzia),transmission is a passive process initiated by the contamination ofwater with excreta containing parasite eggs, and ending with thepenetration by the infective larvae (cercariae) of the skin of peoplein contact with that water. From a disease control perspective,however, the term vector is used generously to include all species