Fig. 2 shows a simple water treatment system used on a farm to purify water taken from a river before it is used for livestock. (a) Name the processes takin...

Labelled answer diagram:

(a) The three stages of the water treatment system are: [3]

1. Stage A - Sedimentation (settling). Large suspended particles of soil, sand and debris settle to the bottom of a tank under gravity. [1]
2. Stage B - Filtration. Water passes through a filter medium (such as sand and gravel) that traps smaller particles remaining after sedimentation. [1]
3. Stage C - Chlorination (disinfection). Chlorine is added to the water to kill microorganisms. [1]

(b) Stage A (sedimentation) must be carried out before Stage B (filtration) because: [2]

• Sedimentation allows the large, heavy particles of soil, sand and organic debris to settle to the bottom of the tank first. [1]
• If these large particles were not removed, they would block or clog the pores of the filter material in Stage B, making filtration much less effective and requiring frequent filter replacement. [1]

(c) The purpose of adding chlorine at Stage C: [2]

• Chlorine kills harmful bacteria, viruses and other microorganisms that may still be present in the water after sedimentation and filtration. [1]
• This makes the water safe for livestock to drink by preventing the transmission of waterborne diseases such as E. coli infections, salmonellosis and other gastrointestinal illnesses. [1]

(d) Three ways a farmer can reduce the risk of contamination of a farm well: [3]

1. Build a raised concrete wall or apron around the well opening to prevent surface runoff (which may carry animal waste, soil or chemicals) from flowing directly into the well. [1]
2. Place a secure cover or lid over the well to stop debris, insects, small animals and rainwater from falling in. [1]
3. Keep livestock and manure storage away from the immediate area around the well to prevent faecal contamination of the groundwater. [1]

Other acceptable measures include: avoiding storing or applying farm chemicals (pesticides, fertilisers) near the well; locating pit latrines and waste disposal sites at least 30 metres from the well.