1. A guide for GCSE students KNOCKHARDY PUBLISHING
WATER
A guide for GCSE students
2010 SPECIFICATIONS
KNOCKHARDY PUBLISHING

2. WATER INTRODUCTION www.knockhardy.org.uk
This Powerpoint show is one of several produced to help students understand selected GCSE Chemistry topics. It is based on the requirements of the AQA specification but is suitable for other examination boards.
Individual students may use the material at home for revision purposes and it can also prove useful for classroom teaching with an interactive white board.
Accompanying notes on this, and the full range of AS and A2 Chemistry topics, are available from the KNOCKHARDY WEBSITE at...
All diagrams, photographs and any animations in this Powerpoint are original and created by Jonathan Hopton. Permission must be obtained for their use in any work that is distributed for financial gain.

3. WATER CONTENTS Properties of water
Occurrence of water – The water cycle
Hardness of water – the causes
Temporary hardness
Permanent hardness
Removing permanent hardness in water
Hard water – advantages and disadvantages
Water pollution and its treatment

4. PROPERTIES OF WATER GENERAL INFORMATION
Structure Water consists of covalent molecules of formula H2O.
Physical colourless, odourless liquid.
properties boils at 100°C freezes at 0°C
(if pure and at atmospheric pressure)
Chemical Reacts with some metals to produce hydrogen.
properties
Uses Essential for life.
An important solvent.
A coolant for many industrial processes (e.g. power stations)
Raw material in the manufacture of ammonia.
Raw material in the conversion of ethene to ethanol.
Test Turns blue cobalt chloride pink or
Turns white anhydrous copper(II) sulphate blue.

5. water ——> hydrogen (2 vols) + oxygen (1 vol)
COMPOSITION OF WATER
Fill both limbs of a Hofmann Voltameter with
water which has been acidified with a small
amount of dilute sulphuric acid. Pass sufficient
direct current through the apparatus to enable
measurable amounts of gas to be collected.
ANODE (+) - a colourless gas collected
- the gas re-lit a glowing splint
CATHODE (-) - a colourless gas collected
- its volume was twice that at anode
- gas exploded with a squeaky pop when a lighted splint was applied
Conclusion Water can be split into its elements
by passing electricity through it.
water ——> hydrogen (2 vols) oxygen (1 vol)
Dilute sulphuric acid is added to improve the conductivity of the water.

6. OCCURRENCE
Water is the most abundant substance on the surface of our planet.

7. RESOURCE FOR INDUSTRIAL PROCESSES
OCCURRENCE
Water is the most abundant substance on the surface of our planet.
Importance LIVING SYSTEMS
RESOURCE FOR INDUSTRIAL PROCESSES

8. RESOURCE FOR INDUSTRIAL PROCESSES
OCCURRENCE
Water is the most abundant substance on the surface of our planet.
Importance LIVING SYSTEMS
RESOURCE FOR INDUSTRIAL PROCESSES
Occurrence OCEANS
LAKES
RIVERS
ATMOSPHERE - clouds and water vapour

9. RESOURCE FOR INDUSTRIAL PROCESSES
OCCURRENCE
Water is the most abundant substance on the surface of our planet.
Importance LIVING SYSTEMS
RESOURCE FOR INDUSTRIAL PROCESSES
Occurrence OCEANS
LAKES
RIVERS
ATMOSPHERE - clouds and water vapour
Water Cycle Shows the inter- relationship between water
in different environments.

10. Shows the inter- relationship between water in different environments.
THE WATER CYCLE
Shows the inter- relationship between water in different environments.
Water evaporates from
seas, lakes and rivers and
from the leaves of plants.
The water vapour produced
condenses to form clouds
and later falls as rain, hail
and snow.
The rain and snow complete
the cycle by flowing down
streams and rivers into lakes
or seas.
Some water seeps through
rocks and soils to join
underground reservoirs.

11. PURITY OF WATER
Natural water is never pure. It is such a good solvent that it contains dissolved
substances whatever its origin.
RAIN dissolved gases from the air e.g. CO2, SO2
RIVERS dissolved salts from rocks and soils; also oxygen.
SEA dissolved sodium and magnesium salts (e.g. NaCl) and CO2
water also
contains man-made chemicals such as detergents, acids,
fertilizers and other pollutants.

12. “Hard water is water which does not readily form a lather with soap”
WHAT IS HARDNESS?
“Hard water is water which does not readily form a lather with soap”

13. WHICH IONS CAUSE HARDNESS?
“Hard water is water which does not readily form a lather with soap”
Method
Place a sample of one of the solutions in a test-tube to a depth of about 2cm.
Using a dropping pipette, place a measured amount of soap solution into the
water and shake vigorously for five seconds. Record the height of the lather.
Repeat with another sample; decide which ions are responsible for hardness.

14. WHICH IONS CAUSE HARDNESS?
“Hard water is water which does not readily form a lather with soap”
Method
Place a sample of one of the solutions in a test-tube to a depth of about 2cm.
Using a dropping pipette, place a measured amount of soap solution into the
water and shake vigorously for five seconds. Record the height of the lather.
Repeat with another sample; decide which ions are responsible for hardness.
A sodium sulphate
B magnesium sulphate
C potassium chloride
D calcium chloride
E sodium nitrate
F magnesium nitrate
G calcium nitrate
H sodium chloride
A B C D E F G H

15. WHICH IONS CAUSE HARDNESS?
“Hard water is water which does not readily form a lather with soap”
Method
Place a sample of one of the solutions in a test-tube to a depth of about 2cm.
Using a dropping pipette, place a measured amount of soap solution into the
water and shake vigorously for five seconds. Record the height of the lather.
Repeat with another sample; decide which ions are responsible for hardness.
A sodium sulphate
B magnesium sulphate
C potassium chloride
D calcium chloride
E sodium nitrate
F magnesium nitrate
G calcium nitrate
H sodium chloride
A B C D E F G H

16. WHICH IONS CAUSE HARDNESS?
“Hard water is water which does not readily form a lather with soap”
Method
Place a sample of one of the solutions in a test-tube to a depth of about 2cm.
Using a dropping pipette, place a measured amount of soap solution into the
water and shake vigorously for five seconds. Record the height of the lather.
Repeat with another sample; decide which ions are responsible for hardness.
Solution used ions present lather
+ ive - ive
A sodium sulphate Na+ SO42- YES
B magnesium sulphate Mg SO42- NO
C potassium chloride K+ Cl- YES
D calcium chloride Ca2+ Cl- NO
E sodium nitrate Na+ NO3- YES
F magnesium nitrate Mg2+ NO3- NO
G calcium nitrate Ca2+ NO3- NO
H sodium chloride Na+ Cl- YES
Conclusions The ion(s) responsible for hardness is / are...

17. WHICH IONS CAUSE HARDNESS?
“Hard water is water which does not readily form a lather with soap”
Method
Place a sample of one of the solutions in a test-tube to a depth of about 2cm.
Using a dropping pipette, place a measured amount of soap solution into the
water and shake vigorously for five seconds. Record the height of the lather.
Repeat with another sample; decide which ions are responsible for hardness.
Solution used ions present lather
+ ive - ive
A sodium sulphate Na+ SO42- YES
B magnesium sulphate Mg SO42- NO
C potassium chloride K+ Cl- YES
D calcium chloride Ca2+ Cl- NO
E sodium nitrate Na+ NO3- YES
F magnesium nitrate Mg2+ NO3- NO
G calcium nitrate Ca2+ NO3- NO
H sodium chloride Na+ Cl- YES
Conclusions The ion(s) responsible for hardness is / are... Ca2+ and Mg2+

18. HARD WATER – HOW DOES IT ARISE?
Definition “Water that does not readily form a lather with soap”.
Instead, it forms an unsightly scum.
Causes Arises from the solvation of compounds out of rocks / soils.
The compounds are SOLUBLE magnesium or calcium salts.

19. HARD WATER – HOW DOES IT ARISE? SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS
Definition “Water that does not readily form a lather with soap”.
Instead, it forms an unsightly scum.
Causes Arises from the solvation of compounds out of rocks / soils.
The compounds are SOLUBLE magnesium or calcium salts.
ROCKS CONTAINING
SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS
LIMESTONE
(CALCIUM CARBONATE)
WATER

20. HARD WATER – HOW DOES IT ARISE?
Definition “Water that does not readily form a lather with soap”.
Instead, it forms an unsightly scum.
Causes Arises from the solvation of compounds out of rocks / soils.
The compounds are SOLUBLE magnesium or calcium salts.
RAIN DISSOLVES THE SOLUBLE SALTS IN ROCKS
ROCKS CONTAINING
SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS
LIMESTONE
(CALCIUM CARBONATE)
WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

21. HARD WATER – HOW DOES IT ARISE? SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS
Definition “Water that does not readily form a lather with soap”.
Instead, it forms an unsightly scum.
Causes Arises from the solvation of compounds out of rocks / soils.
The compounds are SOLUBLE magnesium or calcium salts.
LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO2
ROCKS CONTAINING
SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS
LIMESTONE
(CALCIUM CARBONATE)
WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

22. HARD WATER – HOW DOES IT ARISE?
Definition “Water that does not readily form a lather with soap”.
Instead, it forms an unsightly scum.
Causes Arises from the solvation of compounds out of rocks / soils.
The compounds are SOLUBLE magnesium or calcium salts.
RAIN DISSOLVES THE SOLUBLE SALTS IN ROCKS
LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO2
ROCKS CONTAINING
SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS
LIMESTONE
(CALCIUM CARBONATE)
WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

23. HARD WATER – HOW DOES IT ARISE?
Definition “Water that does not readily form a lather with soap”.
Instead, it forms an unsightly scum.
Causes Arises from the solvation of compounds out of rocks / soils.
The compounds are SOLUBLE magnesium or calcium salts.
RAIN DISSOLVES THE SOLUBLE SALTS IN ROCKS
LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO2
ROCKS CONTAINING
SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS
LIMESTONE
(CALCIUM CARBONATE)
WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

24. HARD WATER – HOW DOES IT ARISE?
Definition “Water that does not readily form a lather with soap”.
Instead, it forms an unsightly scum.
Causes Arises from the solvation of compounds out of rocks / soils.
The compounds are SOLUBLE magnesium or calcium salts.
There are TWO main types of hardness…

25. HARD WATER – HOW DOES IT ARISE?
Definition “Water that does not readily form a lather with soap”.
Instead, it forms an unsightly scum.
Causes Arises from the solvation of compounds out of rocks / soils.
The compounds are SOLUBLE magnesium or calcium salts.
There are TWO main types of hardness…
PERMANENT HARDNESS
TEMPORARY HARDNESS

26. TEMPORARY HARDNESS

27. SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS
TEMPORARY HARDNESS
Source Atmospheric carbon dioxide dissolves in rain water making
an acidic solution which reacts with limestone (calcium
carbonate). Soluble calcium hydrogencarbonate is formed.
CaCO3(s) CO2(g) H2O(l) ——> Ca(HCO3)2(aq)
LIMESTONE IS INSOLUBLE IN WATER BUT DOES DISSOLVE IN RAIN WHICH IS ACIDIC DUE TO DISSOLVED CO2
ROCKS CONTAINING
SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS
LIMESTONE
(CALCIUM CARBONATE)
WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

28. TEMPORARY HARDNESS
Source Atmospheric carbon dioxide dissolves in rain water making
an acidic solution which reacts with limestone (calcium
carbonate). Soluble calcium hydrogencarbonate is formed.
CaCO3(s) CO2(g) H2O(l) ——> Ca(HCO3)2(aq)
Removal Boiling the water reverses the above reaction.
A white precipitate of insoluble calcium carbonate is
produced. The calcium is thus removed from the water.
Ca(HCO3)2(aq) ——> CaCO3(s) CO2(g) H2O(l)

29. TEMPORARY HARDNESS REMEMBER
Source Atmospheric carbon dioxide dissolves in rain water making
an acidic solution which reacts with limestone (calcium
carbonate). Soluble calcium hydrogencarbonate is formed.
CaCO3(s) CO2(g) H2O(l) ——> Ca(HCO3)2(aq)
Removal Boiling the water reverses the above reaction.
A white precipitate of insoluble calcium carbonate is
produced. The calcium is thus removed from the water.
Ca(HCO3)2(aq) ——> CaCO3(s) CO2(g) H2O(l)
plus Any method used for removing permanent hardness.
REMEMBER
Only water containing SOLUBLE calcium and magnesium ions causes hardness.

30. TEMPORARY HARDNESS REMEMBER
Source Atmospheric carbon dioxide dissolves in rain water making
an acidic solution which reacts with limestone (calcium
carbonate). Soluble calcium hydrogencarbonate is formed.
CaCO3(s) CO2(g) H2O(l) ——> Ca(HCO3)2(aq)
Removal Boiling the water reverses the above reaction.
A white precipitate of insoluble calcium carbonate is
produced. The calcium is thus removed from the water.
Ca(HCO3)2(aq) ——> CaCO3(s) CO2(g) H2O(l)
plus Any method used for removing permanent hardness.
REMEMBER
Only water containing SOLUBLE calcium and magnesium ions causes hardness.

31. PERMANENT HARDNESS

32. PERMANENT HARDNESS
Source Soluble calcium and magnesium compounds which dissolve
in streams and rivers as they pass over and through rocks
and soils.
RAIN DISSOLVES THE SOLUBLE SALTS IN ROCKS
ROCKS CONTAINING
SOLUBLE CALCIUM OR MAGNESIUM COMPOUNDS
LIMESTONE
(CALCIUM CARBONATE)
WATER CONTAINING SOLUBLE CALCIUM OR MAGNESIUM IONS

33. PERMANENT HARDNESS magnesium chloride MgCl2 magnesium sulphate MgSO4
Source Soluble calcium and magnesium compounds which dissolve
in streams and rivers as they pass over and through rocks
and soils.
SOLUBLE calcium chloride CaCl2
magnesium chloride MgCl2
magnesium sulphate MgSO4
INSOLUBLE calcium carbonate CaCO3
magnesium carbonate MgCO3

34. PERMANENT HARDNESS magnesium chloride MgCl2 magnesium sulphate MgSO4
Source Soluble calcium and magnesium compounds which dissolve
in streams and rivers as they pass over and through rocks
and soils.
SOLUBLE calcium chloride CaCl2
magnesium chloride MgCl2
magnesium sulphate MgSO4
INSOLUBLE calcium carbonate CaCO3
magnesium carbonate MgCO3
REMEMBER
Only water containing SOLUBLE calcium and magnesium ions causes hardness.

35. PERMANENT HARDNESS - REMOVAL
DISTILLATION

36. PERMANENT HARDNESS - REMOVAL
DISTILLATION
Boil the water and collect pure water as the distillate. All the dissolved solids
will be left behind. This is the only method to produce pure water.
However, it is an expensive method
because of the energy requirements.
CONDENSER
PURE WATER
HARD WATER

37. PERMANENT HARDNESS - REMOVAL
ION-EXCHANGE RESIN

38. PERMANENT HARDNESS - REMOVAL
ION-EXCHANGE RESIN
• Ion-exchange resins are special compounds containing Na+ or H+ ions
• Hard water contains soluble calcium and/or magnesium ions
RESIN

39. PERMANENT HARDNESS - REMOVAL
ION-EXCHANGE RESIN
• Ion-exchange resins are special compounds containing Na+ or H+ ions
• Ca2+and Mg2+ ions in the hard water swap with those on the resin
• The water comes out with Na+ ions in it
• Ca2+and Mg2+ ions remain attached to the resin
• Na+ and H+ ions do not cause hardness.
Ca2+(aq) Na+ ——> Ca Na+(aq)
in hard water on resin on resin in softened water
RESIN

40. PERMANENT HARDNESS - REMOVAL
ION-EXCHANGE RESIN
• Ion-exchange resins are special compounds containing Na+ or H+ ions
• Eventually, all the Na+ ions get used up so the resin must be replaced or
flushed through with sodium chloride solution to replace the calcium.
RESIN

41. PERMANENT HARDNESS - REMOVAL
SOAP

42. PERMANENT HARDNESS - REMOVAL
SOAP
Soap molecules have two distinctly different ends;
HYDROPHOBIC HYDROPHILIC
“water hating” “water liking”
attracts oil and grease attracts water
CHAIN OF CARBON ATOMS

43. PERMANENT HARDNESS - REMOVAL
SOAP
Soap molecules have two distinctly different ends;
HYDROPHOBIC HYDROPHILIC
“water hating” “water liking”
attracts oil and grease attracts water
When soap is placed in hard water, it reacts with the calcium and
magnesium ions to produce an unsightly, insoluble grey scum.
CHAIN OF CARBON ATOMS

44. PERMANENT HARDNESS - REMOVAL
SOAP
Soap molecules have two distinctly different ends;
HYDROPHOBIC HYDROPHILIC
“water hating” “water liking”
attracts oil and grease attracts water
When soap is placed in hard water, it reacts with the calcium and
magnesium ions to produce an unsightly, insoluble grey scum.
The scum is a calcium compound and is thus removed from the water.
When all the hardness has been removed, the soap can act in the normal way.
CHAIN OF CARBON ATOMS

45. PERMANENT HARDNESS - REMOVAL
SOAP
Soap molecules have two distinctly different ends;
HYDROPHOBIC HYDROPHILIC
“water hating” “water liking”
attracts oil and grease attracts water
CHAIN OF CARBON ATOMS
In HARD WATER AREAS it is better to use SOAPLESS DETERGENTS which have structures similar to soap.
Detergents form a lather without forming a scum.
Because of this they DO NOT REMOVE HARDNESS.

46. PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate)

47. PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate)
is one of the few
soluble carbonates -
it is a good source
of soluble carbonate
ions.

48. PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate)
is one of the few
soluble carbonates -
it is a good source
of soluble carbonate
ions.
Hard water contains
soluble calcium
(or magnesium)
ions.

49. PERMANENT HARDNESS - REMOVAL
WASHING SODA (sodium carbonate)
Sodium carbonate
is one of the few
soluble carbonates -
it is a good source
of soluble carbonate
ions.
Add the two solutions in
order to mix the ions.
Hard water contains
soluble calcium
(or magnesium)
ions.

50. PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate)
The Ca2+ and CO32- ions
come together to form a
precipitate of insoluble
calcium carbonate.
The calcium ions are
removed from the water
so it is now soft.

51. PERMANENT HARDNESS - REMOVAL WASHING SODA (sodium carbonate) - SUMMARY
Sodium carbonate is one of the few soluble carbonates
- it is a good source of soluble carbonate ions.
Addition of washing soda to a solution containing magnesium
ions or calcium ions results in the precipitation of insoluble carbonates.
Once the magnesium, or calcium, has been removed from the water,
the water is no longer hard - it is soft.
equation CaCl2(aq) Na2CO3(aq) ——> 2NaCl(aq) CaCO3(s)
ionic equation Ca2+(aq) CO32-(aq) ——> Ca2+CO32-(s)

52. HARD WATER Disadvantages
Furring up of pipes and boilers; the heating is not as effective
blockages may lead to an explosion

53. HARD WATER Disadvantages
Furring up of pipes and boilers; the heating is not as effective
blockages may lead to an explosion
Furring up of kettle elements; wastes electricity

54. HARD WATER Disadvantages
Furring up of pipes and boilers; the heating is not as effective
blockages may lead to an explosion
Furring up of kettle elements; wastes electricity
Wastes soap; as some is needed to remove the hardness
unsightly scum is formed during washing

55. HARD WATER Disadvantages
Furring up of pipes and boilers; the heating is not as effective
blockages may lead to an explosion
Furring up of kettle elements; wastes electricity
Wastes soap; as some is needed to remove the hardness
unsightly scum is formed during washing
Advantages calcium strengthens teeth and bones.
better for preventing heart diseases

56. WATER POLLUTION

57. WATER POLLUTION Origin nitrates and phosphates in farm fertilizers
animal waste products
industrial chemical waste
lead ions (Pb2+) from old pipes

58. WATER POLLUTION Origin nitrates and phosphates in farm fertilizers
animal waste products
industrial chemical waste
lead ions (Pb2+) from old pipes
Effects Nitrates from fertilizers encourage plant and algae growth.
When algae die they are decomposed by aerobic bacteria
which need oxygen. The oxygen is thus removed from the
water making the river “dead” and incapable of supporting
fish populations.
Nitrates can also be converted to nitrites (which affect
haemoglobin in blood) and into carcinogenic nitrosamines.
Industrial waste can be in many forms including cyanide,
detergents and heavy metals and radioactive products.
A build up of lead can lead to brain damage.

59. WATER POLLUTION Origin nitrates and phosphates in farm fertilizers
animal waste products
industrial chemical waste
lead ions (Pb2+) from old pipes
Effects Nitrates from fertilizers encourage plant and algae growth.
When algae die they are decomposed by aerobic bacteria
which need oxygen. The oxygen is thus removed from the
water making the river “dead” and incapable of supporting
fish populations.
Nitrates can also be converted to nitrites (which affect
haemoglobin in blood) and into carcinogenic nitrosamines.
Industrial waste can be in many forms including cyanide,
detergents, heavy metals and radioactive products.
A build up of lead can lead to brain damage.

60. WATER PURIFICATION

61. WATER PURIFICATION
Water of the correct quality is essential for life. For humans, drinking
water should have sufficiently low levels of dissolved salts and microbes.

62. WATER PURIFICATION
Water of the correct quality is essential for life. For humans, drinking
water should have sufficiently low levels of dissolved salts and microbes.
Filtration removes insoluble organic matter;
the sludge is digested to produce methane.
Aeration removes organic waste using oxygen-requiring bacteria.
Chlorination kills bacteria to allow water to be used for drinking purposes.

63. IT CAN THEN BE SENT TO HOUSES THROUGH THE MAINS
WATER PURIFICATION
Water of the correct quality is essential for life. For humans, drinking
water should have sufficiently low levels of dissolved salts and microbes.
Filtration removes insoluble organic matter;
the sludge is digested to produce methane.
Aeration removes organic waste using oxygen-requiring bacteria.
Chlorination kills bacteria to allow water to be used for drinking purposes.
IT CAN THEN BE SENT TO HOUSES THROUGH THE MAINS

64. OTHER THINGS THAT CAN BE DONE
WATER PURIFICATION
Water of the correct quality is essential for life. For humans, drinking
water should have sufficiently low levels of dissolved salts and microbes.
Filtration removes insoluble organic matter;
the sludge is digested to produce methane.
Aeration removes organic waste using oxygen-requiring bacteria.
Chlorination kills bacteria to allow water to be used for drinking purposes.
OTHER THINGS THAT CAN BE DONE
Fluoridation Fluoride compounds are added to water in some areas to aid
the prevention of tooth decay. The fluoride is only helpful to
children and can be given in tablet form. Many people object
to the addition of fluoride to drinking water.

65. OTHER THINGS THAT CAN BE DONE
WATER PURIFICATION
Water of the correct quality is essential for life. For humans, drinking
water should have sufficiently low levels of dissolved salts and microbes.
Filtration removes insoluble organic matter;
the sludge is digested to produce methane.
Aeration removes organic waste using oxygen-requiring bacteria.
Chlorination kills bacteria to allow water to be used for drinking purposes.
OTHER THINGS THAT CAN BE DONE
Fluoridation Fluoride compounds are added to water in some areas to aid
the prevention of tooth decay. The fluoride is only helpful to
children and can be given in tablet form. Many people object
to the addition of fluoride to drinking water.
Water filters These contain carbon, silver and ion exchange resins and
can remove some dissolved substances from tap water to
improve the taste and quality.

66. OTHER THINGS THAT CAN BE DONE
WATER PURIFICATION
Water of the correct quality is essential for life. For humans, drinking
water should have sufficiently low levels of dissolved salts and microbes.
Filtration removes insoluble organic matter;
the sludge is digested to produce methane.
Aeration removes organic waste using oxygen-requiring bacteria.
Chlorination kills bacteria to allow water to be used for drinking purposes.
OTHER THINGS THAT CAN BE DONE
Fluoridation Fluoride compounds are added to water in some areas to aid
the prevention of tooth decay. The fluoride is only helpful to
children and can be given in tablet form. Many people object
to the addition of fluoride to drinking water.
Water filters These contain carbon, silver and ion exchange resins and
can remove some dissolved substances from tap water to
improve the taste and quality.
Distillation Needs a lot of energy so is expensive but makes the purest water.

67. © 2011 JONATHAN HOPTON & KNOCKHARDY PUBLISHING
WATER
THE END
© JONATHAN HOPTON & KNOCKHARDY PUBLISHING