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1、4.WATERSAMPLINGANDANALYSIS4.WatersamplingandanalysisIdeally,alaboratoryinfrastructureshouldbeestablishedwhichwillenableallsamplestobereturnedtoacentralorregionallaboratorywithinafewhoursofbeingtaken.However,thisdependsontheavailabilityofagoodroadsystemandofreliablemotorizedtransportfor
2、allsamplingofficers,andthesearenotavailableinmanycountries.Thus,althoughitmaybepossibletoestablishwell-equippedcentralandevenregionallaboratoriesforwateranalysis,attheprovincialanddistrictlevelsitmaybenecessarytorelyonarelativelysmallnumberofsimpletests.AsnotedinChapter1,thisapproachiss
3、ometimescalledcritical-parameterwatertesting.Themostimportantfactortotakeintoaccountisthat,inmostcommunities,theprincipalrisktohumanhealthderivesfromfaecalcontamination.Insomecountriestheremayalsobehazardsassociatedwithspecificchemicalcontami-nantssuchasfluorideorarsenic,butthelevelsofth
4、esesubstancesareunlikelytochangesignificantlywithtime.Thus,ifafullrangeofchemicalanalysesisundertakenonnewwatersourcesandrepeatedthereafteratfairlylongintervals,chemicalcontaminantsareunlikelytopresentanunrecognizedhazard.Incon-trast,thepotentialforfaecalcontaminationinuntreatedorinadeq
5、uatelytreatedcommunitysuppliesisalwayspresent.Theminimumlevelofanalysisshouldthereforeincludetestingforindicatorsoffaecalpollution(thermotolerant(faecal)coliforms),turbidity,andchlorineresidualandpH(ifthewaterisdisinfectedwithchlorine).Evenindevelopingcountriespoorlyservedbyroadsandtra
6、nsportation,itisusuallypossibletodevisearationalsamplingandanalyticalstrategy.Thisshouldincorporatecarefullyselectedcritical-parametertestsinremote(usuallyrural)locationsusingsimplemethodsandportablewater-testingequipment(seepp.65–66)whereappropriate.Whereverpossiblethecommunityshouldb
7、einvolvedinthesamplingprocess.Wherewaterisdisinfected,primaryhealthworkers,schoolteachers,andsometimescommunitymemberscanbetrainedtocarryoutsimplechlorineresidualtesting.Thesamepeoplecouldalsocollectsamplesforphysicochemicalanalysisandarrangefortheirdeliverytotheregionallaboratory.Th
