Water Distribution Systems
Distribution fundamentals
Distribution questions blend hydraulics with operations. Know pipe materials (PVC, ductile iron, HDPE), valve types (gate, butterfly, check, pressure-reducing), hydrants, storage (elevated, ground, hydropneumatic), and how pressure is created and lost. Pressure comes from elevation head and pumps; friction loss grows with flow and pipe roughness (Hazen-Williams C-factor). Florida rules require a minimum of 20 psi under all conditions and typically 35–40 psi normal operating pressure; fire flow needs drive main sizing.
Cross-connection and water quality
Backflow prevention (air gaps, RPZ, DCVA, PVB) protects the system. Water age causes disinfectant decay and DBP formation, so utilities flush dead ends, cycle storage, and manage tank levels. Distribution sampling for coliform and disinfectant residual must be at representative sites.
Traps
- 1 psi = 2.31 ft of water; 1 ft = 0.433 psi.
- Confusing static pressure with residual pressure during flow.
- Forgetting that a check valve allows one direction only.
- Mixing up gate (isolation) and globe/butterfly (throttling) uses.
Worked example
A tank water surface is 100 ft above a hydrant. Static pressure = 100 ÷ 2.31 = 43.3 psi. If friction loss to the hydrant is 8 psi, residual pressure at the same flow is 35.3 psi.
Rule of thumb
Every 2.31 ft of elevation equals 1 psi. Use it to check any pressure answer for reasonableness.