雅思阅读第005套P3-THE SEARCH FOR FRESH WATER

READING PASSAGE 3

You should spend about 20minutes on Questions 27-40, which are based on Reading Passage 3.

THE SEARCH FORFRESH WATER

The assertion that water hasalways been the essence of life is nothing new. Water comes in many forms:spring water, sea and river water, rainwater, and fog and dew water. Yet wateris becoming scarce and this scarcity is becoming a very real worry forgovernments all around the world. The reality is that one of the main obstaclesto the economic development of a particular country is its lack of an adequatesupply of fresh water. Current figures show that an inhabitant of a wealthy,modern town consumes 100-400 litres of water daily. In some developingcountries the amount of water consumed does not exceed 20-30 litres per day.Rich or poor, annual water consumption has continued to grow, increasingfourfold over the last 50 years.

The world’s fresh watersupplies are drawn from a number of sources. The largest cache of the estimated35 million km3 fresh water reserve is located in glaciers and snow. The amountcontained in these 'storehouses’ has been estimated to be around 24 millionkm3. Ground water is also a big contributor to the world’s fresh water suppliesamounting to an estimated 10.5 million km3. Considering that the total volumeof water, salt and fresh, is estimated to be around 400 million km3 it can beclearly seen that the amount of fresh water available in the world is only theproverbial 'drop in the bucket՝. Artesian wells, rivers and lakes only accountfor about 0.1 and 0.5 million km3 respectively, all of which includeatmospheric precipitation such as rain and snow.

Since water is such animportant commodity, various attempts to acquire stores of it have been triedwith varying degrees of success. The question of what are the alternative watersources available to us today is not an easy one to answer but is certainlyworthy of our best efforts to find one. One such area of interest has beendesalination – the turning of salt water into drinkable water. As there is muchmore salt water on the earth than dry land, the idea of using desalinatedseawater seems a logical one. However, some estimates put the annual quantityof desalinated water at only around ten cubic kilometres – a tiny amount giventhe amount of sea water available. In parts of Senegal, for example, thegreenhouse effect has been one way to desalinate seawater whereby the salt inthe water is separated from the water through a process of evaporation. As partof the process, water vapour forms on large panes of glass at outside airtemperature and is transported via gravity into drums. This method yields onlya few cubic meters per day of fresh water but is surprisingly energy efficient.In larger scale production however, the energy efficiency plummets. The bestsystems bum at least a tonne of fossil fuel to produce approximately onehundred cubic metres of fresh water. This amounts to almost $ 1 per cubic metre– a considerable cost.

Although there are severaldifferent areas from which water can be sourced, paradoxically the mostextensive are the most difficult to tap. The atmosphere, for example, containsvast amounts of fresh water composed of 2% condensed water in the form ofclouds and 98% water vapour. The vastness of this water source is comparable tothe renewable liquid water resources of all inhabited lands. The amounts areeasy to calculate, but being able and knowing how to economically obtain thiswater in liquid form is most challenging. One approach in drawing water fromthe atmosphere is fog nets. Places such as the coastal desens of West Africaand areas of Chile and Peru have favourable condensation conditions. In theseareas, ocean humidity condenses in the form of fog on the mid-range mountains(over 500m). This fog composed of droplets of suspended water can be collectedin nets. In the 1960s, a University in Northern Chile conducted the first majorexperiments with fog nets. Drawing on the knowledge gained from theseexperiments, further testing was done which culminated in one village using fognets to yield a healthy daily average of 11,000 litres of water. On a smallerscale, fog-collecting nets have recently been used in the Canary Islands andNamibia.

Unfortunately, due to its needfor a combination of several factors, fog is not readily available. Dew howeverappears far more frequently and is less subject to the constraints of climateand geography. In order for dew to form there needs to be some humidity in theair and a reasonably clear sky. Many hot areas of countries that suffer from alack of water such as the Sahel region of Northern Africa for example,experience significant quantities of dew. When the temperature is lowered overa short space of time by ten degrees or so, the water-harvesting possibilitiesfrom the air yield an amazing ten grams of water from each cubic meter of air –significant drops in air temperature make for greater yields. Unlike fog, dewformation can occur even in a relatively dry atmosphere, such as a desert. Allit takes is for the right mix of temperatures between the earth and the air tocombine and dew formation occurs.

SECTION 3: QUESTIONS 27-40

Questions 27-29

Choose the correctletter, A, B. C or D

Write your answers inboxes 27-29 on your answer sheet.

27As a method of obtaining fresh water, fog

Aforms best when the air is dry.

Bis easier to collect than dew.

Cis being tried in a large-scaleway in Senegal.

Dis not easy to collect.

28Small-scale 'greenhouse effect’desalination

Auses a considerable amount ofenergy.

Bis the most effective way toobtain larger water reserves.

Cuses very little energy.

Dburns quite a lot of fossilfuel.

29One of the largest stores of fresh waterin the world is

Arivers and lakes.

Batmospheric rain and snow.

Cground water.

Dartesian wells

Questions 30-34

Complete each sentence with thecorrect ending A-F from the box below.

Write the correct letter A-F inboxes 30-34 on your answer sheet.

A

is quite popular due to it not being too affected by temperature and location.

B

is being tried via an evaporation process.

C

is not energy efficient.

D

is best for poorer countries.

E

is made up of both clouds and water vapour.

F

is increased when temperatures fall rapidly.

30 ____________ Turning salt water into drinkingwater

31 ____________ Large-scale fresh water productionthrough evaporation

32 ____________ Water available in the atmosphere

33 ____________ The use of dew as a water source

34 ____________ The amount of water collected fromdew

Questions 35-40

Do the following statementsagree with the information given in Reading Passage 3?

In boxes 35-40 onyour answer sheet, write

TRUE

if the statement agrees with the information

FALSE

if the statement contradicts the information

NOT GIVEN

If there is no information on this

35 ________________ The amount of water consumed bywealthier countries is just as much as poorer countries.

36 ________________ Glaciers, rivers, artesianwells and ground water are all sources of fresh water.

37 ________________ Large bodies of water, such asthe sea, have yielded the most fresh water.

38 ________________ The collection of water throughthe use of fog nets is becoming increasingly more popular around the world.

39 ________________ If the sky is cloudy, dew willnot form.

40 ________________N Dew and fog are majorsources of water in smaller villages and isolated areas.