Question 1

What's a typical C-factor?

Accepted Answer

New PVC: 150. New DI: 140. New cast iron: 130. 20-year cement-lined DI: 130. 50-year unlined CI: 70–100.

Question 2

Why does C drop over time?

Accepted Answer

Tuberculation (iron oxide nodules), biofilm, and CaCO₃ scale increase roughness and shrink effective diameter — both lower C and raise head loss.

Question 3

Can low C be fixed without replacement?

Accepted Answer

Yes. Pipe cleaning (drag scrapers, pigs) followed by cement-mortar lining restores C to ~130. Cured-in-place lining is another option.

Question 4

Is C the same as roughness ε?

Accepted Answer

Different concept. C is empirical for water in Hazen-Williams. ε (roughness in feet) is used in Darcy-Weisbach friction-factor calculations.

Hazen-Williams C-Factor Back-Calculation