Glossary

The vocabulary of hydraulics for water networks.

In short — The terms of drinking-water network modelling, each defined in one or two sentences: hydraulics, water quality, transients and operations.

.inp file: EPANET's text format describing a complete network: nodes, pipes, pumps, valves, curves, controls and calculation options. It is the industry's reference exchange format.
Cavitation: The formation of vapour pockets when local pressure falls to the vapour pressure of water. In a pump, it erodes the impellers; in a pipe, it can break the water column.
Digital twin: A hydraulic model continuously connected to measurements from the real network (SCADA, sensors) to compare the computed state with the measured state and detect leaks and anomalies.
Extended-period simulation: A series of hydraulic calculations over a period — often 24 hours — during which demands follow demand patterns and tanks fill and empty.
Global gradient method: A method for solving the hydraulic balance of a looped network, computing node heads and pipe flows together through Newton iterations. It is the method used by EPANET, and by ORCANET.
Hazen-Williams formula: An empirical formula for friction head loss, the most widely used for drinking water. Its C coefficient describes roughness: about 140 for a new smooth pipe, less for an old one.
Head loss: The energy water loses as it flows, expressed in metres of water column: through friction along the pipes, and locally in bends, valves and fittings.
Model calibration: Adjusting a model's uncertain parameters — roughness, demands, set points — so that computed pressures and flows match those measured in the field.
NPSH: Net positive suction head of a pump, above vapour pressure. The NPSH available from the installation must exceed the NPSH required by the pump, otherwise the pump cavitates.
Pressure reducing (PRV): A valve that holds a constant downstream pressure whatever the upstream pressure, to protect a low-lying zone of a network. EPANET and ORCANET call it a PRV.
Residual chlorine: The concentration of chlorine remaining in the water at a point in the network, after decay in the bulk water and at the pipe wall. It must stay above a threshold to guarantee disinfection.
Service pressure: The pressure available at the delivery point during operation. A study checks it at each node against an allowable minimum (often 20 m) and maximum.
Tank: An elevated reservoir that stores water and sets the head of a network zone. It fills during off-peak hours and releases water at the peak; its level swing is tracked in extended-period simulation.
Water age: The time elapsed since the water left its source. A high age signals stagnant water, where chlorine runs out and quality deteriorates.
Water hammer: A surge and low-pressure wave caused by a sudden change in flow in a pressurised pipe — a valve closing, a pump stopping. It travels at the wave speed and can burst a pipe or cause cavitation.
Wave speed: The speed at which a pressure wave travels along a pipe, around 1,000 m/s in steel or cast iron and 300 m/s in PVC. It depends on the compressibility of water and the elasticity of the pipe wall.