1.1. Water can be made potable by treating water from lakes and rivers.

What does potable water mean?

1.2. The first stage in treating water from rivers and lakes removes solid particles such as soil, twigs and small pebbles.

What is the name of the process used in this stage?

1.3. Another stage of water treatment is to sterilise the water.

What could not be used to sterilise the water?

Tick (✓) one box.

1.4. Sea water can be made safe to drink by desalination.

Distillation can be used to desalinate sea water.

The equipment that could be used to desalinate sea water is shown in Figure 1.

Figure 1

Give the names of the components A to E.

1.5. Desalination of sea water is an expensive process so it is only used to produce large quantities of drinking water when there is no alternative supply.

Give one reason why the process is so expensive?