The rate of flow equals the cross-sectional Area of the pipe

Multiplied by the velocity of the water movement Through it, or **Q = AV **Where

Q = volume of flow past a given point per unit of time

A = cross-sectional area of the pipe or conduit

V = velocity of fluid travel in terms of distance per unit of time

Most water distribution systems are sized for a velocity of 3 to 6 ft/s

(0.9 to 1.8 m/s) or for a pressure loss of 1 to 5 lb/in2 per 100 ft of piping.

In this range, flow is turbulent and fine particulates usually stay in suspension.

There is variation in the velocity: pressure loss relationship between small and

large diameter piping,Increased roughness of piping with age, as corrosion or scale

develops, also affects this ratio.

Pipe fittings and valves introduce additional pressure loss, which

provides a basis for estimating overall pressure loss and pumping requirements

for water distribution systems.

Wastewater collection piping is usually larger than freshwater distribution

systems because it frequently must carry off its flow by gravity alone.