For modeling purposes, these system elements are organized into the following categories:

• Pipes—Transport water from one location (or node) to another.
• Junctions/Nodes—Specific points, or nodes, in the system at which an event of interest is occurring. This includes points where pipes intersect, where there are major demands on the system such as a large industry, a cluster of houses, or a fire hydrant, or critical points in the system where pressures are important for analysis purposes.
• Reservoirs and Tanks—Boundary nodes with a known hydraulic grade that define the initial hydraulic grades for any computational cycle. They form the baseline hydraulic constraints used to determine the condition of all other nodes during system operation. Boundary nodes are elements such as tanks, reservoirs, and pressure sources.
• Pumps—Represented as nodes. Their purpose is to provide energy to the system and raise the water pressure.
• Valves—Mechanical devices used to stop or control the flow through a pipe, or to control the pressure in the pipe upstream or downstream of the valve. They result in a loss of energy in the system.

An event or condition at one point in the system can affect all other parts of the system. While this complicates the approach that the engineer must take to find a solution, there are some governing principles that drive the behavior of the network, including the Conservation of Mass and Energy Principle, and the Energy Principle.

The two modes of analysis are Steady-State Network Hydraulics and Extended Period Simulation. This program solves for the distributions of flows and hydraulic grades using the Gradient Algorithm.