节约用水(Saving Water)

详细内容

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theworldisnotonlyhungry,butalsothirstyforwater.thismayseemstrangetoyou,sincenearly75%oftheearth'ssurfaceiscoveredwithwater.butabout97%ofthishugeamountisseawater,orsaltwater.

mancanonlydrinkandusetheother3%--thefreshwaterthatesfromrivers,lakes,underground,andothersources.andwecannotevenuseallofthat,becausesomeofitisintheformoficebergsandglaciers.evenworse,someofithasbeenpolluted.

however,asthingsstandtoday,thissmallamountoffreshwater,whichisconstantlybeingreplacedbyrainfall,isstillenoughforus.butourneedforwaterisincreasingrapidly--almostdaybyday.onlyifwetakestepstodealwiththisproblemnowcanweavoidasevereworldwidewatershortagelateron.

alimitedwatersupplywouldhaveabadeffectonagricultureandindustry.letmegiveyoujustonesmallexampieofhownecessarywateristoindustry.didyouknowthattoproduceasingletonofsteel,ittakesabout91,000litersofwater?

weallhavetolearnhowtostopwastingourpreciouswater.oneofthefirststepsweshouldtakeistodevelopwaysofreusingit.experimentshavealreadybeendoneinthisfield,butonlyonasmallscale.forus,thesystemsareasimportantasthespacecraft.