1. 1
   A UK water company sources fresh water from a reservoir and treats it in stages to produce potable water for a nearby town.

   (a)

   Which statement correctly describes potable water?

   [1 mark]

   • AWater safe to drink, with sufficiently low levels of dissolved salts and microbes
   • BWater containing no dissolved substances at all
   • CWater that has been distilled to remove all ions
   • DWater taken directly from the sea without treatment

   (b)

   At the treatment works, the water passes through beds of sand and gravel before sterilisation. What is the main purpose of this stage?

   [1 mark]

   • ATo kill all microbes in the water
   • BTo filter out solid particles and larger debris
   • CTo add dissolved salts to improve taste
   • DTo remove all dissolved oxygen from the water

   (c)

   After filtration, the water company sterilises the water using chlorine. Explain why sterilisation is a necessary step in producing potable water, and name one alternative method of sterilisation that could be used.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A coastal town in a hot, dry region has very little fresh water available, so it treats sea water to produce potable water using desalination.

   (a)

   Which process uses a partially permeable membrane to separate salts from water under pressure?

   [1 mark]

   • AReverse osmosis
   • BFractional distillation
   • CChromatography
   • DElectrolysis

   (b)

   Which of the following is a disadvantage of producing potable water by distillation of sea water compared with treating fresh water from a reservoir?

   [1 mark]

   • AIt cannot remove any dissolved salts
   • BIt requires large amounts of energy to evaporate the water
   • CIt produces water that is unsafe to drink
   • DIt only works on fresh water, not sea water

   (c)

   Explain why desalination of sea water is generally more expensive than producing potable water from fresh water sources such as reservoirs.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A school science class is given two labelled samples of water: Sample X is described as "pure water" and Sample Y is described as "potable water". The class is asked to design a simple test to check the purity of Sample X.

   (a)

   Explain the difference between pure water and potable water.

   [3 marks]

   (b)

   Describe a method the class could use to test whether Sample X is genuinely pure water, and explain how the results would show whether the sample is pure.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A government is planning the water supply for a growing city. Option 1 is to expand treatment of fresh water from an inland reservoir using filtration and chlorination. Option 2 is to build a large desalination plant using reverse osmosis on sea water, since the reservoir alone cannot supply enough water for the growing population.

   (a)

   A government is planning water supply for a growing city. Option 1 is to expand treatment of fresh water from an inland reservoir using filtration and chlorination. Option 2 is to build a large desalination plant using reverse osmosis on sea water, since the reservoir alone cannot supply enough water for the growing population. Discuss the factors the government should consider when choosing between these two options for producing potable water.

   [6 marks]

   (b)

   Environmental campaigners argue that the desalination plant (Option 2) should not be built because of its high energy use, and instead suggest the city should reduce water demand through conservation measures alongside the existing reservoir supply. Evaluate this argument, considering whether conservation alone could meet the city's growing water needs.

   [6 marks]

   Total for question 4: 12 marks

End of questions