The Depth Crossover Between Hand-Dug Wells and Drilled Boreholes: Cost per Reliable Litre Against Water-Table Depth, and the Pump-Class Step at the Suction Limit

Total cost per reliable litre over 15 years is computed for hand-dug wells and drilled boreholes as a function of water-table depth (3-40 m) at a stated demand of 4,000 L/day, carrying digging rate decay, lining, dewatering, depth-rising failure probability, and the pump-class change at the 7 m suction limit. At US$6 per day labour the dug well wins until a crossover at 27.2 m (US$0.087 vs US$0.313 per 1,000 L at 3 m; US$1.115 vs US$0.519 at 40 m). Crossing the suction limit raises dug-well cost from US$0.109 to US$0.194 per 1,000 L across 0.2 m of depth. The crossover moves to 29.7 m at US$3/day labour and 23.7 m at US$12/day. SIMULATED, NOT MEASURED.