Water, Water Ev€rywhere . . .
73
Themw material
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Although water is not a ‘universal solvent’, comparatively few
materials remain una’ected by prolonged contact with it. Conse—
quently, the water in rivers, streamsand wells carries dissolved
mineral salts washed out from the rocks over which it has passed. In
fact accurate measurementof the mineral Salts dissolved in a stream
coupled with a knowledge of its course provides a relatively cheap
way of geological surveying and prospecting. Generally, theiwater
in rivers and streams has quite a low mineral content because most
of the easily dissolved materials have been washed away…long ago.
Before this water is ready to drink, debris, any dangerous baCteria
and undesirable odours and taste must be removed. Well—water and
other standing waters which have spent some time in contact with
the ground usually present the additioalproblemof large—quanties
of dissolved materials. Frequently, matter dissolved in this water
exceeds 500 parts per million -(,p.p.m.) by weight, the
for
potable water. Since the composition depends “largely on the
materials with which the water comes into contact, brackishwaterS
varÿ considerably in salinity and mineral “content. For example,
water at Buckeye (Arizona) has a salinity of 2,200 p.,p.m., at Bahrein;
it is 3,400 ;p.p.m. and at Welko‘m (South Africa),3,ooo p.p.m.
,
Sea—water also '
varies both in total salt… content and composition,
but the uctuationsare not as great as thoseof brackish waters.;—In
theopen «oceans, away from the inueceof river estuaries, the total
dissolved mineral content is about 35,600 p.p.m. In_more.conned
areas such as the Red Sea this increases to about 43,000 p.p.‘m.,The
table below shows that although in this
discussed largely in terms of…sodiumchloride, there…is far _more;,in
'
COMPOSITION OF
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”AppÏbximatê parcenmgè
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Sodium
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30
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Sulphate ;;
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8
…Magnesium
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4 …:
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Potassrum.
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