About EPANET
We have no connection to the people or agency that made EPANET. If anything here is wrong, EPA’s own page is the authority and this one is not.
About EPANET, the model this is built on
EPANET performs extended-period simulation of the hydraulic and water-quality behaviour of pressurized pipe networks. You describe a system of junctions, reservoirs, tanks, pipes, pumps, and valves; it computes the pressure at every junction, the flow in every pipe, the level in every tank, and the fate of a chemical or of the water's own age as it travels through the network. It can simulate a moment (steady state) or a week (extended period simulation).
It was created by Lewis A. Rossman for the United States Environmental Protection Agency's water research programme, and first appeared in 1993, with a formal report on the EPANET water quality model published the same year. EPANET 2 followed. Version 2.2 was the last release made by EPA itself.
It is used by utilities, consulting engineers, regulators, and universities all over the world, and its computational engine is embedded in a large number of other programs, commercial and free, this one included. It is the most widely used model of its kind.
Why it costs nothing, and what that means
EPANET costs nothing because United States copyright law does not permit a work of the federal government to be copyrighted at all. 17 U.S.C. § 105 says copyright protection is not available for any work of the United States government, and a work of the United States government is defined as one prepared by an officer or employee as part of that person's official duties.
The practical consequences are unusual:
- There is no license to accept. Public domain is not a license. There is nothing to agree to and no terms to comply with.
- There is no owner to ask. Nobody can grant or withhold permission, because nobody holds the right that permission would come from.
- Anybody may do anything, including take it private. A company may build EPANET into a product and sell it, and need not publish what it changed. Many have. That is the deliberate design of the public domain, not a loophole in it.
- It cannot be withdrawn. No future decision by anybody can make the existing code less available than it is today.
Our own project made the opposite choice, GNU GPL v3 or later, and says so in honesty item 2, because it is a restriction EPA did not impose.
Who develops it now
After EPA's 2.2, EPANET's development continued in the open at Open Water Analytics, a community effort in collaboration with EPA. Version 2.3 was released on 2024-07-17 and 2.3.5 on 2025-02-20. The engine our network editor runs is OWA-EPANET 2.3.5, which is why a run report from our page prints a version number higher than the one on EPA's download page.
If you want EPANET, get EPANET
This site exists to point you at something built on the EPANET legacy. Use EPANET itself if you need the reference implementation, if you need a feature we do not have, if your reviewer expects EPANET output, or if you prefer it. It is free, it is the reference implementation, it is still being developed in the open, and it does not need our permission or our approval, any more than we need EPANET's.
What we could not verify
EPA’s 2.2 was released around early 2020. That is an approximation and is written as one: the sources we checked give different exact dates and we did not resolve which is right, so a precise date appears nowhere on this site. We have also not verified the exact administrative name of the EPA division EPANET was developed in, which sources give differently, so it is described here only as EPA’s water research programme.