Hazen-Williams C — Pipe Roughness Reference
For pressurized water-distribution head loss: hf = 4.52·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 |
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.