Larger pipe sizes significantly reduce friction losses in apartment water distribution systems by allowing water to flow at lower velocities. This minimizes turbulence and pressure drops, ensuring consistent supply across multiple units.
Friction Loss Principles
Friction loss occurs as water rubs against pipe walls, increasing with smaller diameters, higher flow rates, and longer runs. The Hazen-Williams equation shows loss drops dramatically with diameter increases: ΔP ∝ 1/D^1.17, where D is internal diameter. For borehole-fed apartments, aim for velocities under 2.5 m/s to avoid noise and erosion.
Recommended Pipe Sizes
Use these sizes based on flow demand from borehole pumps (e.g., 10-20m³/hour for 50 units):
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Main supply line (borehole to tank): 50-65mm (2-2.5″) for 15m³/h, cutting loss by 50% vs 40mm.
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Branch lines to floors: 32-40mm (1.25-1.5″) per 10-15 units.
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Individual apartment feeds: 25-32mm (1-1.25″) to maintain 1-2 bar pressure.
Material and Layout Tips
Opt for smooth PE or PVC pipes (C-factor 150) over galvanized steel to halve losses. Minimize elbows (add 5-10m equivalent length each) and use sweep bends. For multi-apartment risers, step down sizes gradually: 63mm main to 40mm per floor.
In Kenyan complexes like those served by Raeli Hydro, upsizing mains from 40mm to 50mm saves 3-5m TDH, matching pumps like Grundfos SQ perfectly while boosting ROI through lower energy use.