Before modeling water supply networks, you must have a basic understanding of the terminology used when discussing water flow and velocity.

Pressure Flow — a unit of volume moving past a certain point within a unit of time. Flow is measured in different units, depending upon its application.
Velocity — the distance of a given fluid within a unit of time, or how fast a fluid is moving.
Flow — equivalent to the velocity of the water multiplied by the radius of the pipe squared. The smaller the pipe, the greater the velocity at the same flowrate.
Low velocities can result in sediment deposits, while changes in velocity can lift and release these deposits.
Flow moving through smooth, unobstructed pipework will move at a constant velocity and is known as laminar flow.

The formula for flow, with definitions for each symbol displayed. A diagram of a pipe that begins wide and narrows on the other side demonstrates changes in velocity.

Headloss — the combination of energy losses within a pipe, such as frictional contact with the pipe wall or bends in the pipe.

A diagram showing a pipe with directional flow. Two pipes connect at the top of the pipe, showing headloss from one to the other.

Turbulent flow — flow that is disrupted by bends or roughness of a pipe wall.
Losses — increase velocities and flowrates, requiring more energy to overcome. Losses are usually measured per distance. In WS Pro, the Darcy-Weisbach equation is used to calculate headloss.
Hydraulic transient (a.k.a. surge, water hammer) — in water networks, refers to pressure changing with time and typically reflects rapid or unexpected changes in pressure.

A graph showing rapid changes to pressure over a span of time.

Understanding pipes

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