water quality

Question 1

potable water

Answer 1

water that is safe to drink and cook with, containing no pathogens or toxic substances

Question 2

desalination

Answer 2

removal of salt and impurities from sea water and to make it suitable for drinking

Question 3

two approaches to produce potable water

Answer 3

• distillation
• reverse osmosis

Question 4

distillation

Answer 4

evaporation of water followed by the resulting water vapour’s condensation to produce pure (distilled) water

Question 5

osmosis

Answer 5

natural tendency of water to diffuse through a semi-permeable membrane from a solution of low salt concentration to one of higher salt concentration

Question 6

reverse osmosis

Answer 6

high pressure is used to force water through a semi-permeable membrane in the opposite way water naturally flows, where water moves from a solution of high salt concentration to a very low salt concentration solution (fresh water)

Question 7

semi-permeable membrane

Answer 7

a membrane that allows water molecules to pass through but not larger molecules or salt ions

Question 8

where does this water come from?

Answer 8

• groundwater
• seawater
• surface water

Question 9

3 criteria for potable water

Answer 9

1. levels of dissolved substances need to be fairly low
2. no micro-organisms
3. pH needs to be between 6.5 to 8.5

Question 10

groundwater treatment

Answer 10

aeration: spraying groundwater to expel gases as they often contain dissolved gases like CO2 and H2S
clarification: removal of fine particles by adding aluminium sulfate and calcium oxide which causes suspended particles to clump together
sand filtration: water passes through filter beds of granulated anthracite and sand to remove fine suspended particles
disinfection: chlorine is added to destroy harmful pathogenic bacteria and viruses that may be present
fluoridation: adjusting the natural fluoride concentration as fluoride ions reduce tooth cavity rates by strengthening tooth enamel
pH: australian guidelines specify a pH range of 6.5 to 8.5 pH, correction is achieved by the addition of line (CaO) (for increasing pH) or by dissolving carbon dioxide gas, CO2 (lowers pH)

Question 11

TDS

Answer 11

total dissolved salts

Question 12

freshwater treatment

Answer 12

1. filter out any big things with a wire mesh
2. bed of sand and gravel which filters out other smaller bits
3. sterilising the water to kill any microbes by bubbling chlorine gas through it