'Potable' and 'pure' water are not the same substance.
Water used in analysis must not contain any dissolved ions.
The method used to obtain potable water depends on the water source.
Sedimentation, filtration and chlorination are used to obtain potable water from groundwater and fresh water sources.
Desalination of seawater creates potable water by distillation or reverse osmosis.

Common misconception

Pupils tend to think that all water is the same. Pupils tend to forget that non-visible substances are also found in water.

Stress that pure water only contains H₂O molecules. Other types of water may include varying amounts of dissolved salts, other solids or micro-organisms. Stress that microbes must be killed for water to be potable, but are too difficult to remove.

Keywords

Pure - A single element or compound that is not mixed with any other substance.
Potable - Water that is safe to drink.
Sterilisation - The process of killing bacteria and other living microorganisms.
Desalination - The process of removing dissolved salts from seawater.
Reverse osmosis - The movement of solvent through a semipermeable membrane by applying excess pressure on the solution. This process can remove dissolved solutes from water.

Create a circus activity about the different types of water (e.g. information posters) and challenge pupils to consider what methods might be used to create potable water from them.

Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Video

Skip video

Worksheet

Download worksheet

Skip worksheet

Starter quiz

Download starter quiz

6 Questions

Q1.

The equipment setup shown below shows which separation technique?

decanting

Correct answer: filtration

distillation

chromatography

Q2.

Match each letter on the diagram below to the correct label.

Correct Answer:a,filtrate

filtrate

Correct Answer:b,funnel

funnel

Correct Answer:c,filter paper

filter paper

Correct Answer:d,residue

residue

Q3.

A single element or compound that is not mixed with any other substance is said to be .

Correct Answer: pure

Q4.

A substance that dissolves into another substance is described as .

Correct Answer: soluble

Q5.

When a substance dissolves into a liquid (e.g. water), a __________ forms.

suspension

Correct answer: solution

solute

solvent

Q6.

Which of the following techniques can be used to fully isolate components of a mixture or solution?

decanting

Correct answer: filtration

Correct answer: distillation

crystallisation

Exit quiz

Download exit quiz

6 Questions

Q1.

Water is essential for life. Which of the following are domestic uses of water?

watering crops

Correct answer: washing laundry

hydrating farm animals

Correct answer: cooking

Q2.

All sources of water contain varying amounts of micro-organisms and what other material?

insoluble solids

salt

Correct answer: dissolved substances

Q3.

Water that is safe to drink is classified as .

Correct Answer: potable

Q4.

Match each step of making potable water, from either groundwater or freshwater, to the correct description.

Correct Answer:screening,A grid acts like a sieve, removing large insoluble objects.

A grid acts like a sieve, removing large insoluble objects.

Correct Answer:sedimentation,Small, insoluble particles 'settle out', forming a sediment.

Small, insoluble particles 'settle out', forming a sediment.

Correct Answer:filtration,Very small particles are removed by passing through fine layers.

Very small particles are removed by passing through fine layers.

Correct Answer:sterilisation,Microbes are killed.

Microbes are killed.

Q5.

What is used to sterilise a water sample to ensure it is potable?

Correct Answer: chlorine, chlorine gas, Cl, Cl₂

Q6.

Put the following stages of creating potable water from groundwater or freshwater in the correct order.

1 - screening

2 - sedimentation

3 - filtration

4 - sterilisation