New borehole: pumping test, hybrid solar pumping, fluoride and operating costs

Drawdown: 60 − 42 = 18 m. Specific capacity: 12 / 18 = 0.67 m³/h per metre of drawdown. The level stabilised and recovery is fast (95% in 6 h): the aquifer recharges adequately at this rate.

Operating yield: 0.7 × 12 = 8.4 m³/h.

Pump intake: at least 60 + 10 = 70 m; there is still a margin for the seasonal drop in water level, with a measured bottom at 120 m.

Depth of 120 m: the borehole remains usable, as the pump is installed well above the bottom. But the 30 m gap with the 150 m invoiced and declared as cased is either over-invoicing (borehole shallower than declared) or infilling of the bottom (collapse or sand, a sign of poor borehole construction or development, which can damage the pump). This must be checked before any payment: new measurement in the presence of the contractor, camera inspection if possible, comparison with the delivery notes for the casing and the drilling log, analysis of turbidity and sand content of the pumped water.

Need: 9,600 × 15 L = 144 m³/day. F3 supplies 40 m³: F7 must supply 104 m³/day.

Pumping: 104 / 8.4 = 12.38 h per day. Solar: 7 h × 8.4 = 58.8 m³. Remaining 104 − 58.8 = 45.2 m³, i.e. 45.2 / 8.4 = 5.38 h of generator per day, and 5.38 × 4 = 21.52 L of diesel per day. Adding panels does not extend the hours of sunshine: the flow is capped at 8.4 m³/h by the borehole, so the solution is hybrid or requires another source.

Storage: 50% × 104 = 52 m³. The 45 m³ tank is 7 m³ short; at least one 10 m³ tank must be added (margin), all the more so as solar pumping takes place during the day while demand is concentrated in the morning and evening.

Taps: Sphere: no more than 250 people per tap, based on a flow of 7.5 L/min. 9,600 / 250 = 38.4, i.e. 39 taps. Existing: 6 × 4 = 24; 15 are missing, i.e. 4 additional tapstands with 4 taps each (40 taps in total), less than 500 m from the shelters.

Distribution time: 39 × 7.5 = 292.5 L/min; 144,000 / 292.5 = 492 min, i.e. 8.2 h per day, compatible with two distribution slots, provided that network pressure ensures 7.5 L/min at each tap. With 40 taps: 8 h.

The water is bacteriologically safe (E. coli 0); nitrate is well below the guideline value; the high conductivity of F7 may affect the taste and reduce acceptability (risk of people returning to unprotected sources), with no health-based value. F7 fluoride (1.9 mg/L) exceeds the guideline value of 1.5 mg/L: risk of dental fluorosis and, with prolonged and higher exposure, skeletal fluorosis; this risk relates to long-term exposure, not an immediate danger.

Blend: (104 × 1.9 + 40 × 0.8) / 144 = (197.6 + 32) / 144 = 1.59 mg/L, slightly above 1.5.

Maximum volume from F7: (x × 1.9 + 40 × 0.8) / (x + 40) = 1.5, hence 1.9x + 32 = 1.5x + 60, i.e. 0.4x = 28 and x = 70 m³/day. Total 110 m³, i.e. 11.46 L per person per day.

Decision: the choice is between 144 m³ at 1.59 mg/L and 110 m³ at 1.5 mg/L. In a population of new arrivals, lack of water has immediate health effects (hygiene-related diseases): it is defensible to supply 15 L/p/d with water at 1.59 mg/L on a temporary basis, after informing and obtaining the agreement of the health authorities, with a dated plan to return below 1.5 mg/L: new low-fluoride source, defluoridation, or F3 water reserved for drinking. Regular fluoride measurement at the tank, monitoring among children. Never present the blended water as compliant.

Diesel: 21.52 L × 365 = 7,856 L, i.e. 7,856 × 1.40 = 10,999 USD. Operators: 2 × 150 × 12 = 3,600. Maintenance: 2,500. Chlorination: 1,200. Total: 18,299 USD per year.

Annual volume: 144 × 365 = 52,560 m³; 0.35 USD per m³. Per household: 18,299 / 12 / 1,920 = 0.79 USD per month. Fuel accounts for 60% of the cost.

Options: (1) reduce fuel costs: new source or additional borehole equipped with solar to eliminate the generator, which also solves the fluoride problem; (2) budget operation in subsequent funding and negotiate its takeover by the agency responsible for the site and the county authorities (public service approach, gradual integration); (3) trained water management committees, with the participation of women, and possibly a modest contribution, after analysing ability to pay, without excluding the most vulnerable households (access to water must not depend on payment); (4) maintenance contracts and stock of spare parts; (5) functionality monitoring through indicators (breakdown rate, repair time, actual cost per m³).

I do not pay the full amount until the discrepancy has been explained. I propose to the contractor to pay the undisputed portion without delay (120 m, i.e. 21,600 USD, if the contract allows it, and the other undisputed items) and to withhold the disputed 5,400 USD (30 m × 180) pending a joint measurement.

I reply courteously to the representative: we value local companies and we will pay what is owed, quickly, but in line with our procedures, which also protect the community (a poorly constructed borehole breaks down). I do not give in to pressure and I make a note of the call.

As for the technician: I do not conclude that he was complicit. He may have signed without being present at the end of drilling. I gather his account, I check and, if there is a suspicion of collusion, I report it in line with the anti-fraud policy. I strengthen controls: mandatory presence at the final measurement, joint measurement signed by two people, check of the casing delivered.