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Primary General Studies: Water Treatment and Public Health (Paper 3 (challenge))
Primary General Studies: Water Treatment and Public Health (Paper 3 (challenge))
This is the challenge paper, handling harder calculations on dosing, leakage, capacity and cost.
Direct answers Show the unit conversion at every step, since swapping cubic metres and litres is where most marks are lost.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: Primary General Studies: Water Treatment and Public Health |
| Level | P5 |
02 Questions (10 items)
- FoundationChlorine is dosed at 2 milligrams per litre. How many kilograms are needed for 1,000 cubic metres?
- FoundationOf 4,800,000 cubic metres supplied, 25 per cent leaks from the pipes. How much reaches users?
- FoundationWhy is rapid mixing used in the coagulation stage?
- IntermediateWhy is a small chlorine residual kept at the far ends of the distribution network?
- IntermediateWhy is fluoride added to drinking water?
- IntermediateWhy must drinking water and sewage be handled completely separately?
- ChallengeA works can produce 600,000 cubic metres a day. The city has 2,000,000 people using 130 litres each. What spare capacity is left?
- ChallengeTreatment costs 8.5 dollars per cubic metre and output is 400,000 cubic metres a day. What is the daily cost?
- ChallengeA reservoir holds 30,000,000 cubic metres and the city uses 1,000,000 a day. How many days can it last without rain?
- Error redoError clinic: why is the claim that more chlorine means safer water wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 2 kilograms. | 1,000 cubic metres is 1,000,000 litres, times 2 milligrams gives 2,000,000 milligrams, that is 2,000 grams or 2 kilograms. |
| 2 | 3,600,000 cubic metres. | 4,800,000 times 0.25 is 1,200,000 lost, and the remaining 3,600,000 reaches users. |
| 3 | So the alum spreads evenly and meets the suspended particles. | Poor mixing leaves the flocs too small, which spoils both settling and filtration. |
| 4 | To stop the water being re-contaminated inside the pipes. | Even clean water can grow microbes along long mains, so the residual is the last line of defence. |
| 5 | To reduce tooth decay. | Fluoride hardens the tooth surface, but the dose must be controlled because too much affects how teeth look. |
| 6 | Sewage carries many pathogens, so mixing it into drinking water spreads disease. | Gut infections such as cholera and typhoid can all travel through contaminated water. |
| 7 | 340,000 cubic metres. | 2,000,000 people times 130 litres is 260,000,000 litres or 260,000 cubic metres, and 600,000 minus 260,000 leaves 340,000. |
| 8 | 3,400,000 dollars. | 400,000 times 8.5 is 3,400,000, and the cost moves with raw water quality and energy prices. |
| 9 | 30 days. | 30,000,000 divided by 1,000,000 is 30, which is why the dry season needs water saving and imported supply. |
| 10 | Excess chlorine forms disinfection by-products and bad taste, so the dose must be tightly controlled. | Disinfection needs enough contact time and residual, not simply more chlorine. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
Drinking water goes from reservoir through coagulation, settling, sand filtration and chlorination while sewage gets screening, settling and aeration in a separate system, with residual chlorine and boiling as the last defence.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.