Hazen-Williams Pipe Head Loss

For water in full pipes: h_f = 10.67 · L · Q^1.852 ÷ (C^1.852 · D^4.87) with Q in m³/s, D in metres and C the roughness coefficient (150 for new plastic, 130 for new steel, 100 for old cast iron). Pressure drop = ρ·g·h_f.