1. Introduction

1.1. What is EPANET

EPANET is a computer program that performs extended period simulation of hydraulic and water quality behavior within pressurized pipe networks. A network consists of pipes, nodes (pipe junctions), pumps, valves and storage tanks or reservoirs. EPANET tracks the flow of water in each pipe, the pressure at each node, the height of water in each tank, and the concentration of a chemical species throughout the network during a simulation period comprised of multiple time steps. In addition to chemical species, water age and source tracing can also be simulated.

EPANET is designed to be a research tool for improving our understanding of the movement and fate of drinking water constituents within distribution systems. It can be used for many different kinds of applications in distribution systems analysis. Sampling program design, hydraulic model calibration, chlorine residual analysis, and consumer exposure assessment are some examples. EPANET can help assess alternative management strategies for improving water quality throughout a system. These can include:

  • Altering source utilization within multiple source systems
  • Altering pumping and tank filling/emptying schedules
  • Use of satellite treatment, such as re-chlorination at storage tanks
  • Targeted pipe cleaning and replacement
Running under Windows, EPANET provides an integrated environment for editing network input data, running hydraulic and water quality simulations, and viewing the results in a variety of formats. These include color-coded network maps, data tables, time series graphs, and contour plots.

1.2. Hydraulic Modeling Capabilities

Full-featured and accurate hydraulic modeling is a prerequisite for doing effective water quality modeling. EPANET contains a state-of-the-art hydraulic analysis engine that includes the following capabilities:

  • Places no limit on the size of the network that can be analyzed
  • Computes friction headloss using the Hazen-Williams, Darcy-Weisbach, or Chezy-Manning formulas
  • Includes minor head losses for bends, fittings, etc.
  • Models constant or variable speed pumps
  • Computes pumping energy and cost
  • Models various types of valves including shutoff, check, pressure regulating, and flow control valves
  • Allows storage tanks to have any shape (i.e., diameter can vary with height)
  • Considers multiple demand categories at nodes, each with its own pattern of time variation
  • Models pressure driven flow issuing from emitters (sprinkler heads)
  • Models pressure driven demand at nodes
  • Can base system operation on both simple tank level or timer controls and on complex rule-based controls

1.3. Water Quality Modeling Capabilities

In addition to hydraulic modeling, EPANET provides the following water quality modeling capabilities:

  • Models the movement of a non-reactive tracer material through the network over time
  • Models the movement and fate of a reactive material as it grows (e.g., a disinfection by-product) or decays (e.g., chlorine residual) with time
  • Models the age of water throughout a network
  • Tracks the percent of flow from a given node reaching all other nodes over time
  • Models reactions both in the bulk flow and at the pipe wall
  • Uses n-th order kinetics to model reactions in the bulk flow
  • Uses zero or first order kinetics to model reactions at the pipe wall
  • Accounts for mass transfer limitations when modeling pipe wall reactions
  • Allows growth or decay reactions to proceed up to a limiting concentration
  • Employs global reaction rate coefficients that can be modified on a pipe-by-pipe basis
  • Allows wall reaction rate coefficients to be correlated to pipe roughness
  • Allows for time-varying concentration or mass inputs at any location in the network
  • Models storage tanks as being either complete mix, plug flow, or two-compartment reactors

By employing these features, EPANET can study such water quality phenomena as:

  • Blending water from different sources
  • Age of water throughout a system
  • Loss of chlorine residuals
  • Growth of disinfection by-products
  • Tracking contaminant propagation events

1.4. Steps in Using EPANET

One typically carries out the following steps when using EPANET to model a water distribution system:

  1. Draw a network representation of your distribution system (see Section 6.2) or import a basic description of the network placed in a text file (see Section 11.4).
  2. Edit the properties of the objects that make up the system (see Section 6.4).
  3. Describe how the system is operated (see Section 6.5).
  4. Select a set of analysis options (see Section 8.1).
  5. Run a hydraulic/water quality analysis (see Section 8.2).
  6. View the results of the analysis (see Section 9).