For pressurized water-distribution head loss: hf = 4.73·L·Q1.852 / (C1.852·D4.87) (US units, hf in ft, L & D in ft, Q in cfs). Use this for water at ~60°F in transmission and distribution mains. For other fluids, low-flow regimes, or where temperature matters, use Darcy-Weisbach instead.
Plastic Pipe
Material
C (new)
C (design)
Notes
PVC, smooth bore
150
140–150
AWWA C900/C905
HDPE, DR 11–17
150
140–150
AWWA C906; very stable with age
Polyethylene, small dia.
140
130–140
service lines
Sizing a whole distribution run, not one pipe? HydroComplete carries C through every reach and ties it back to demand.
Iron & Steel Pipe
Material
C (new)
C (design / aged)
Notes
Ductile iron, cement-mortar lined
140
130–140
AWWA C151/C104; design value typically 130
Ductile iron, unlined (rare)
130
90–110
tuberculation reduces C dramatically
Cast iron, new
130
100–130
Cast iron, 20+ yr unlined
100
60–100
severe tuberculation possible
Steel, cement-mortar lined
140
130–140
AWWA C200/C205
Steel, coal-tar enamel lined
140
130–140
AWWA C203
Steel, riveted (legacy)
110
90–110
Galvanized steel
120
100–120
Concrete & Other
Material
C (new)
C (design / aged)
Notes
Concrete, smooth-formed
130
120–140
Concrete pressure pipe (PCCP)
140
130–140
AWWA C301/C303
Asbestos-cement (legacy)
140
130–140
still in service in older systems
Copper tubing
140
130–140
building service
Brass
130
120–130
Vitrified clay (sewer, full flow)
110
100–120
Design tip — pick the aged value, not the new. A 50-year water main analysis on the C-new value will significantly under-predict head loss. AWWA M22 and most water utility design standards specify the "design" or "aged" C for capacity and pressure-zone analysis. Manufacturers' "C = 150" claim for plastic is for clean, new pipe under controlled conditions.
When to use Hazen-Williams vs. Darcy-Weisbach
Use Hazen-Williams when…
Use Darcy-Weisbach when…
Water at ~50–80°F
Other fluids, hot/cold extremes, viscous flow
Turbulent flow (typical mains)
Laminar / transitional flow (Re < 4000)
Fully-developed water-distribution pipes
Compressible flow, two-phase, complex networks needing energy balance
You need a quick spreadsheet calc
You're modeling in EPANET / WaterCAD / similar (those use D-W internally)
Sources: AWWA M11 (steel), M22 (sizing water service), M23 (PVC), M55 (HDPE). Mays, L.W. (2010). Water Distribution Systems Handbook. Hwang & Houghtalen, Fundamentals of Hydraulic Engineering Systems.
Designing a transmission main? The companion to this table is the
Hazen-Williams equation reference — every form, every unit constant, and the validity limits.
You'll also want
Reynolds number to confirm turbulent regime, and
Manning's n if any of the pipe runs partial-flow as gravity sewer.
For full water-system network analysis with multiple loops and pressure zones, EPANET is free and uses
Darcy-Weisbach internally. For full stormwater modeling that includes pressurized conduits, see
HydroComplete — the SaaS sister product to PE-Calc.
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