Water trucking plan and residual chlorine monitoring

Population: 18,400 people. Requirement: 18,400 × 15 L = 276 m³/day. To be delivered: 276 / (1 - 0.10) = 306.7 m³/day.

Current capacity: (10 + 10 + 15) × 6 rotations = 210 m³/day delivered, i.e. 189 m³ usable after losses, so 189,000 / 18,400 = 10.3 L/person/day. Shortfall: 306.7 - 210 = 96.7 m³/day.

Solutions: one more 15 m³ truck would give 300 m³, still insufficient (14.7 L/p/d). Two more 10 m³ trucks give 210 + 120 = 330 m³ delivered, i.e. 297 m³ usable and 16.1 L/p/d: this is the option to choose. Reducing losses (leaks at the tanks, taps) from 10% to 5% would add about 10 m³/day on the current capacity. In the medium term, cost a solution cheaper than trucking (borehole and network), as water trucking is expensive and vulnerable.

Taps needed = ROUNDUP(population / 250). Missing: B1 7 - 5 = 2; B3 8 - 6 = 2; B6 8 - 6 = 2; B5, B7, B10, B11 and B12: 1 each; B2, B4, B8 and B9: 0. Total: 11 taps (67 existing, 78 needed). Priority to blocks B1 and B3 (330 people per tap), then B6 (312); B10 (280) next.

Classification: within the 0.2 to 0.5 range: B1, B2, B3, B5, B7, B12, i.e. 6 out of 12 (50%). Above 0.5: B4 (0.6), risk of rejection because of the taste. Below 0.2: B6, B8, B9, B10, B11, i.e. 5 out of 12 (42%), water not protected against recontamination.

Probable causes: FRC decreases with storage time and heat: the low values are measured 2 h 30 or more after delivery, or in the afternoon (B11: 9 hours of storage). B9 has a turbidity of 12 NTU: the chlorine demand of turbid water consumes the chlorine (dirty tank or unsettled water), and disinfection is not effective.

Actions: chlorinate at the tank on delivery rather than at loading, adjusting the dose with a jar test; empty, clean and cover the B9 tank and only chlorinate water below 5 NTU; measure FRC on delivery and at the end of the day every day; household-level measurements and promotion of safe storage (clean, closed jerrycans); include these rules in the trucking contract.

Clauses: daily volume and number of rotations per block; single approved water source; tanks reserved for drinking water, cleaned and disinfected before the start and at a set frequency; filling and delivery according to the schedule, delivery notes signed by the tank attendant (time, volume); FRC and turbidity checks by the NGO, refusal of any non-compliant delivery; replacement vehicle within 24 hours in the event of a breakdown; payment per cubic metre delivered and verified, penalties for delays or non-compliance; drivers to comply with the NGO's code of conduct and PSEA policy.

Indicators: (1) L/person/day delivered by block; (2) % of FRC measurements within the 0.2 to 0.5 mg/L range; (3) % of planned rotations completed; (4) number of people per functioning tap; waiting time at the water point can be added, recorded by observation.