现代大学英语精读4第二版Unit-5A--For-Want-of-a-Drink课文原文

ForWantofaDrink1.Whenthewordwaterappearsinprintnowadays,crisisisrarelyfarbehind.Water,itissaid,isthenewoil:aresourcelongsquandered,nowgrowingexpensiveandsoontobeoverwhelmedbyinsatiabledemand.Aquifersarefalling,glaciersvanishing,reservoirsdryingupandriversnolongerflowingtothesea.Climatechangethreatenstomaketheproblemworse.Everyonemustuselesswateriffamine,pestilenceandmassmigrationarenottosweeptheglobe.2.Thelanguageisoftenoverblown,andtheremediessometimesill-conceived,butthebasicmessageisnotwrong.Waterisindeedscarceinmanyplaces,andwillgrowscarcer.Bringingsupplyanddemandintoequilibriumwillbepainful,andpoliticaldisputesmayincreaseinnumberandintensifyintheircapacitytocausetrouble.Tocarryonwithpresentpracticewouldindeedbetoinvitedisaster.3.Why?Thedifficultiesstartwiththesheernumberofpeopleusingthestuff.When,60yearsago,theworld'spopulationwasabout2.5billion,worriesaboutwatersupplyaffectedrelativelyfewpeople.Bothdroughtandhungerexisted,astheyhavethroughouthistory,butmostpeoplecouldbefedwithoutirrigatedfarming.Thenthegreenrevolution,inaninspiredcombinationofnewcropbreeds,fertilizersandwater,madepossibleahugeriseinthepopulation.ThenumberofpeopleonEarthroseto6billionin2000,nearly7billiontoday,andisheadingfor9billionin2050.Theareaunderirrigationhasdoubledandtheamountofwaterdrawnforfarminghastripled.Theproportionofpeoplelivingincountrieschronicallyshortofwaterissettorisefrom8%attheturnofthe21stcenturyto45%by2050.4.Farmers'increasingdemandforwateriscausednotonlybythegrowingnumberofmouthstobefedbutalsobypeople'sdesireforbetter-tasting,moreinterestingfood.Unfortunately,ittakesnearlytwiceasmuchwatertogrowakiloofpeanutsasakiloofsoybeans,nearlyfourtimesasmuchwatertoproduceakiloofbeefasakiloofchicken.With2billionpeoplearoundtheworldabouttoenterthemiddleclass,theagriculturaldemandsonwaterwouldincreaseevenifthepopulationstoodstill.5.Industry,too,needswater.Ittakesabout22%oftheworld'swithdrawals.Domesticactivitiestaketheother8%.Together,thedemandsofthesetwocategoriesquadrupledinthesecondhalfofthe20thcentury,growingtwiceasfastasthoseoffarming.6.Meetingthatdemandisadifficulttask.Onereasonisthatthesupplyofwaterisfinite.Theworldwillhavenomoreofitin2025or2050thanithastoday,orwhenitlappedatthesidesofNoah'sArk.Thisisbecausethelawofconservationofmasssays,broadly,thathoweveryouuseit,youcannotdestroythestuff.Neithercanyoureadilymakeit.Ifsomeofitseemstocomefromtheskies,thatisbecauseithasevaporatedfromtheEarth'ssurface,condensedandreturned.7.Mostofthissurfaceissea,andthewaterbelowit—over97%ofthetotalonEarth—issalty.Inprinciple,thesaltcanberemovedtoincreasethesupplyoffreshwater,butatpresentdesalinationisexpensiveanduseslotsofenergy.8.Ofthe2.5%ofwaterthatisnotsalty,about70%isfrozen,eitheratthepoles,inglaciersorinpermafrost.Soalllivingthings,exceptthoseinthesea,haveabout0.75%ofthetotaltosurviveon.Mostofthisavailablewaterisunderground,inaquifersorsimilarformations.Therestisfallingasrain,sittinginlakesandreservoirsorflowinginriverswhereitis,withluck,replacedbyrainfallandmeltingsnowandice.Thereisalso,takenote,watervaporintheatmosphere.9.Thevalueofwaterasacommodityofcoursevariesaccordingtolocality,purposeandcircumstance.Takelocalityfirst.Waterisnotevenlydistributed—justninecountriesaccountfor60%ofallavailablefreshsupplies—andamongthemonlyBrazil,Canada,Colombia,Congo,IndonesiaandRussiahaveanabundance.Americaisrelativelywelloff,butChinaandIndia,withoverathirdoftheworld'spopulationbetweenthem,havelessthan10%ofitswater.10.Evenwithincountriesthevariationsmaybehuge.TheaverageannualrainfallinIndia'snortheastis110timesthatinitswesterndesert.Andmanyplaceshaveplentyofwater,orevenfartoomuch.Floodingisroutine,andmaybecomemorefrequentanddamagingwithclimatechange.11.Scarceorplentiful,waterisabovealllocal.Itisheavy—onecubicwaterweighsatonne—,soexpensivetomove.Surfacewater—mostlyrivers,lakesandreservoirs—willnotflowfromonebasinintoanotherwithoutartificialdiversion,andusuallyonlywithpumping.Withinabasin,thewaterupstreammaybeusefulforirrigation,industrialordomesticuse.Asitnearsthesea,though,theopportunitiesdiminishtothepointwhereithasnousesexcepttosustaindeltas,wetlandsandtocarrysiltouttosea.12.Theseshouldnotbeoverlooked.Ifriversdonotflow,nothingcanliveinthem.Overafifthoftheworld'sfreshwaterfishspeciesofacenturyagoarenowendangeredorextinct.Halftheworld'swetlandshavealsodisappearedoverthepast200years.Thepointis,though,thatevenwithinabasinwaterismorevaluableinsomeplacesthaninothers.13.Almostanywherearid,thewaterunderground,oncelargelyignored,hascometobeseenasespeciallyvaluableasthedemandsoffarmershaveoutgrowntheirsuppliesofrainandsurfacewater.Groundwaterhascometotherescue,andforawhileitseemedamiraculoussolution:drillaborehole,pumpthestuffupfrombelowandinduecourseitwillbereplaced.Inmanyplaces,however,fromtheUnitedStatestoIndiaandChina,thequantitiesbeingwithdrawnexceedtheannualrecharge.Thisisseriousformillionsofpeoplenotjustinthecountrybutalsoinmanyoftheworld'sbiggestcities,whichoftendependonaquifersfortheirdrinkingwater.14.The20millioninhabitantsofMexicoCityanditssurro