1.10 Potable Water

Question 1

What are the 3 different sources of water we can use to provide potable water?

Answer 1

• Fresh water: either surface water (lakes, rivers, reservoirs), or ground water from aquifers (rocks that trap water underground)
• Waste water: from water that’s been contaminated by human process, e.g. waste water from sewage
• Salt water: from the sea

Question 2

What is included in the criteria that makes water ‘potable’? (3)

Answer 2

• Levels of dissolved substances need to be fairly low
• Has to have a pH of between 6.5-8.5 so its not too acidic or alkaline
• No micro-organisms like bacteria or fungi swimming around

Question 3

What are the 2 benefits of using surface water to provide potable water?

Answer 3

• It’s easy to access
• Replaced frequently by the rain

Question 4

What is a disadvantage of using surface water to provide potable water?

Answer 4

• If its hot and sunny, it can dry up as it is exposed to the sun. In warmer parts of the UK, we often rely on ground water

Question 5

Describe the steps we take to treat ground water in order to make it potable? (2)

Answer 5

• First step is often aeration - the water is mixed with air to increase the levels of dissolved oxygen. This forces other dissolved gases out of the water, and also removes certain ions, which react with the oxygen to form solid oxides
• Then, the water is filtered to remove any solid impurities
• Chlorination

Question 6

What are the steps we take in order to make waste water potable? (3)

Answer 6

• It has to be filtered, which involves multiple steps to remove different sizes of solid impurities
• Next, air is pumped through the water to encourage aerobic bacteria (bacteria that needs oxygen to survive) to grow and break down any organic matter
• For waste water containing toxic substances, additional stages of treatment may involve adding chemicals (e.g. to precipitate metals), UV radiation or using membrane
• Chlorination

Question 7

For waste water that contains toxic substances, what other treatment does it go under in order to make potable water?

Answer 7

Additional stages of treatment may involve adding chemicals (e.g. to precipitate metals), UV radiation or using membranes

Question 8

How is sea water distilled?

Answer 8

• On a big scale, traditional distillation apparatus is used, which usually involves burning fossil fuels to heat the water

Question 9

How is sea water treated using reverse osmosis?

Answer 9

The salt water is forced through a membrane that only allows water molecules to pass through. Ions and larger molecules are trapped by the membrane and so separated from the water

Question 10

What is chlorination? (2)

Answer 10

• Whatever the source, the final step in water treatment is usually chlorination
• Chlorine gas is bubbled through to kill harmful bacteria and other microbes

Question 11

What is a disadvantage of chlorinating water to make it potable?

Answer 11

In certain conditions, chlorine can react with compounds found in the water to form potentially dangerous chemicals. Levels of these chemicals have to be carefully monitored. But because it kills off some really nasty bacteria, the benefits of chlorination are generally thought to far outweigh any risks

Question 12

Where does the UK get most of its potable water from?

Answer 12

Fresh water sources

Question 13

What are 3 sources that are usually sources of fresh water?

Answer 13

• Aquifers
• Rivers
• Lakes

Question 14

What is surface water?

Answer 14

Water that is exposed to the air

Question 15

What is ground water?

Answer 15

Water that is found under the ground, such as in aquifers

Question 16

What are the 3 different ways to sterilise water to kill any microorganisms?

Answer 16

• Bubbling chlorine gas through it
• Exposing it to ozone
• Exposing it to UV radiation

Question 17

What is the main drawback of using desalination to get potable water?

Answer 17

It requires a lot of energy, so is very expensive (and contributes to global warming)