C3.2.2 Purifying water

Question 1

What should drinking water for humans contain?

Answer 1

Low levels of dissolved salts and microbes.

Question 2

How do we produce water of sufficient quality?

Answer 2

Choosing an appropriate source

Passing the water through filter beds to remove any solids

Sterilising with chlorine.

Question 3

Give 4 examples of a good water source.

Answer 3

Lakes
Rivers
Aquifers
Reservoirs.

Question 4

Give a benefit of adding fluorine to drinking water.

Answer 4

Fluoridated water can improve dental health by reducing tooth decay.

Question 5

Give 2 reasons why people say that fluorine should not be added to water.

Answer 5

It has been linked to tooth mottling (staining), bone disease and pain

It forces people to consume fluoride when they drink tap water - taking away their personal choice (making it unethical)

Question 6

What do filter cartridges contain?

Answer 6

Silver to kill bacteria

Carbon (‘activated charcoal’) to absorb impurities, eg chlorine

Ion exchange resins to soften the water, and remove heavy metal ions (such as lead ions)

Question 7

Why do some people like to filter their water?

Answer 7

It removes impurities and this can improve the taste and quality of the water.

Question 8

How is sea water distilled to form pure water?

Answer 8

The seawater is boiled and the water vapour is then cooled and condensed to form pure water, leaving the salt behind.

Question 9

Give 3 disadvantages of distillation.

Answer 9

It is expensive because large amounts of energy are needed to heat the seawater

It increases the use of fossil fuels - which are non-renewable resources

The water contains no dissolved ions and so there are no health benefits.

Question 10

Give 3 advantages of distillation.

Answer 10

Pure water is produced

Provides clean drinking water for those in need

Allows humans to carry on with their lifestyles in countries with little water.