Clear Water, Safe Water? The Borehole and the Stream
After three days of heavy rain, the Basic Science Club at Community Junior Secondary School, Ilesa, collects water samples from two sources used by pupils: the school borehole (covered, with a hand pump) and a stream about 200 m away where some pupils wash their hands and drink. In the laboratory the club finds that the stream sample is cloudy and smells slightly, while the borehole sample is clear and colourless. On this basis the club president writes on the notice board: 'The stream is not safe, but the borehole water is pure and needs no treatment.' A teacher notices that the borehole is only 15 m from the school's pit latrine, and that the school has no electricity and a very small budget. Some pupils already drink the borehole water without boiling it. The club has two weeks to give the school a practical recommendation before the Parents-Teachers Association meeting.
1. Evaluate the president's conclusion. What has the club actually shown, and what has it not shown?
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The club has shown only what the eye and nose can detect: the stream sample is turbid (suspended particles) and has an odour, while the borehole sample is clear and colourless.
That is not evidence that the borehole water is safe. Germs that cause typhoid, cholera and dysentery are invisible, and clear water can carry them. Clear water can also carry dissolved salts and nitrates, which colour and smell do not reveal. One sample from each source on one day is also not representative - rain, use and time of day change water quality.
The teacher's observation makes the warning stronger, not weaker: a borehole 15 m from a pit latrine, especially if the latrine is uphill or the borehole is shallow, can be contaminated by seepage. The correct conclusion is: 'The stream is visibly polluted. The borehole looks clean but has not been shown to be safe, and its position is a risk.' Visible clarity is a starting observation, not a result.
2. Describe a fair test the club could carry out with simple school equipment to compare the two sources.
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A fair test changes only the source of the water and keeps everything else the same.
Collect: the same volume (say 250 ml) in identical clean, rinsed bottles, from each source, at the same time of day, three times over one week.
Test each sample the same way: appearance against a white paper, smell, pH with universal indicator paper, and residue left after evaporating 20 ml on a clean saucer (dissolved solids). If the school has a water-test kit or nutrient broth tubes, do a presence/absence test for bacteria; otherwise send sealed samples to the local water board or general hospital laboratory.
Control: same bottle type, same volume, same observer, same test strip, recorded on the same sheet.
Limit: school tests can show that water is dirty; they cannot prove it is safe. State that in the report, and say which result must come from a laboratory.
3. Recommend a treatment plan to the PTA given no electricity and a small budget, and justify the order of the steps.
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Order matters: remove dirt first, then kill germs, then keep germs out.
- Protect the source. Seal the borehole head, slope the ground so runoff flows away, keep animals away, and note the latrine distance. Treatment cannot fix a source that is being recontaminated daily.
- Settle and filter. Allow water to stand, then pour it through a clean cloth and a bucket of washed sand and gravel. Chlorine is used up by dirt, so this step comes first.
- Disinfect. Boiling is reliable but costs fuel and time. Chlorination with sodium hypochlorite is cheap and works without electricity, but the dose must be right (a few drops per litre, then wait 30 minutes) and the container must be covered. Filtering alone does not kill germs.
- Store safely. Covered container with a tap or ladle, never a cup dipped into the water.
- Teach hand-washing and no drinking from the stream.
The reasoning: each step protects the next. Filtering a chlorinated sample wastes chlorine; storing disinfected water in an open bucket puts the germs straight back.