Potable water

Question 1

What is potable water ?

Answer 1

Water that has been treated or is naturally safe for humans too drink - essential for life

Question 2

Is potable water pure ? Justify your answer

Answer 2

No, pure water contains only H20 molecules whereas potable water can contain lots of other dissolved substances

Question 3

What is the important thing about potable water ?

Answer 3

levels of dissolved salts aren’t too high and PH between 6.5 and 8.5 and also that there are no bacteria.

Question 4

Way potable water is produced 1-2

Answer 4

1) Rainwater is type of freshwater ( not much dissolved in it )

2) When it rains, water can either collect as surface water or as groundwater

Question 5

Way potable water is produced 3 - 4

Answer 5

3) in the UK, the source of fresh water used depends on location. Surface water tends to dry up first so warm area e.g. south-east, most of the domestic water supply comes from groundwater

4) even though it has low levels of dissolved substances, water from these sources still need to be treated to make it safe before use

Question 6

Way potable water is produced 5

Answer 6

5) Filtration - wire mesh screens out large twigs etc, then gravel and sand beds filter out any other solid bits
Sterilisation - done to kill harmful bacteria. Done by bubbling chlorine gas through it or by using ozone or UV light

Question 7

In some dry countries like Kuwait, there’s not enough surface or groundwater and instead seawater must be treated to provide potable water.
How is sea water treated ? 6 -7

Answer 7

6) Distillation can be used to desalinate seawater

7) You can test and purify a sample of water in the lab using distillation ( practical )

• Test pH of water using pH meter - Too high or low then you need to neutralise it, you do this by adding acid or alkali until pH is 7
• set up equipment
• As water in flask heats up, it’ll evaporate and condense as stream
• The drop in temperature inside the condenser, due to the cold water around it steam will condense back into liquid water
• water collected in beaker
• Retest pH of water with pH meter to check its neutral
• You can tell if there were crystals in your initial sample by looking to see if there are remaining crystals in the flask

Question 8

Other processes sea water can be treated by

Answer 8

• use membrane like reverse osmosis
  Salty water passed through membrane that only allows water molecules to pass through, ions and larger molecules trapped by membrane so separated from water

Question 9

Disadvantage of distillation and reverse osmosis

Answer 9

needs loads of energy
expensive
not practical for producing large quantities of fresh water