Borehole Beside the Pit Latrine
A district health officer is investigating a cluster of diarrhoea cases in a farming village. The community's only borehole is 18 m from a pit latrine that is 3.5 m deep; the water table is about 6 m below ground. Recent laboratory results for the borehole are: pH 6.8; turbidity 18 NTU (WHO guideline less than 5 NTU); nitrate 12 mg/L (WHO guideline 50 mg/L); E. coli 14 CFU per 100 mL (WHO guideline 0 CFU per 100 mL). The rainy season has begun and the area around the wellhead is muddy. Some residents say the water looks clear and tastes normal. The clinic recorded seven cases of diarrhoea in children under five in the past two weeks, compared with one case in the previous two weeks. The assembly proposes to chlorinate the borehole once and tell people to continue using it.
1. Interpret the laboratory results and explain which result is the most urgent public-health signal.
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Most urgent result: E. coli 14 CFU/100 mL. The WHO guideline is 0 CFU/100 mL, so the borehole is contaminated with faecal material and poses an immediate risk of diarrhoea, especially to children under five. Turbidity 18 NTU is also above the guideline of less than 5 NTU; turbidity protects microbes from chlorine and makes disinfection less reliable. pH 6.8 is within the usual 6.5–8.5 range, so it is not the main problem. Nitrate 12 mg/L is below the 50 mg/L guideline, so it is not the priority here, although it suggests some pollution load. Clear appearance and normal taste are not safety indicators: E. coli and turbidity can be present in water that looks clear. The cluster of seven cases in two weeks, compared with one previously, supports the laboratory finding rather than contradicting it.
2. Evaluate the assembly's proposal to chlorinate the borehole once and continue using it.
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Chlorinating once is not sufficient. First, turbidity of 18 NTU means chlorine demand is high and microbes can be shielded in particles; a single dose may not achieve disinfection. Second, chlorine has no lasting residual protection in a contaminated borehole, and the source remains 18 m from a pit latrine with a shallow water table (6 m) and muddy wellhead during rains. Third, a single dose does not remove the need to stop recontamination. The proposal may reduce bacterial numbers temporarily, but it could create false reassurance. Continuing to use the water without source protection and household treatment keeps children at risk. Chlorination should be part of a multi-barrier approach, not the whole plan.
3. Recommend a priority action plan for the next two weeks, naming two groups responsible.
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Next two weeks, in priority order: (1) Provide an immediate safe-water option: boil water or use chlorine tablets after filtering/cloth filtration to reduce turbidity; tell families not to drink raw borehole water until retesting. (2) Protect the wellhead: seal the casing, build a concrete apron with drainage, fence the area, and divert runoff away from the borehole. (3) Address the latrine: inspect for leakage, line or relocate it, and keep it at least 30 m from the borehole if possible. (4) Retest for E. coli and turbidity after repairs; treat again only if results justify it. (5) Brief the clinic and community on handwashing, safe storage and symptoms. Responsible groups: District Environmental Health/Assembly for wellhead and latrine enforcement; clinic for surveillance and health education; community water committee for safe-water distribution and maintenance.