Disclosures

1. EPANET is our lineage and our reference

EPANET gave us the file format, the vocabulary, and the answers we are checked against. We built a solver of our own, and it runs extended periods, water quality, every valve type, rules, and patterns itself. EPANET is offered as the default engine setting, and you can choose either one. The specifics, each one listed with its source on the Citations page:

• The file format is EPANET’s. We read and write EPANET’s .inp file, from [TITLE] to [END] across the sections we support, and a value you did not edit comes back out verbatim. We have our own format too: a project saves as JSON, because an .inp cannot hold scenarios, saved profile paths, the background picture itself, map tiles and your view, a Text label with more than one line, or longitude and latitude. Everything an .inp can carry round-trips through one, and the things it cannot are reported rather than dropped.
• The vocabulary is EPANET’s. Junction, reservoir, tank, pipe, pump, valve. Extended period simulation. Trials and iterations, static pressure, drawdown, converge. The four curve types. The grammar of a rule. What happens when you change a unit. An engineer who knows EPANET should not have to learn a second dialect from us, and a build check fails when we start writing one.
• The answers we are measured against are EPANET’s. Our solver was built one piece at a time and matched against EPANET 2.3.5 on every shipped example before each piece was released. Extended period results are also compared against EPA’s own report for its Net3 example network: 2,425 head comparisons across 25 reporting steps, agreeing to 0.005 ft. Water quality is anchored on the same report, worst difference 0.105%. Pump energy is anchored on that report’s own energy table.
• The EPANET engine is still offered, and it is the default. A 679 KB browser build of OWA-EPANET 2.3.5, released 2025-02-20, loaded on demand. It is the setting a new project opens with. You can switch to our built-in solver in the settings.
• Even the arithmetic follows EPANET. Our one Hazen-Williams coefficient pair is derived from EPANET’s h = 4.727 L Q^1.852 / (C^1.852 d^4.871), not from the more commonly quoted metric restatement. The two disagree by up to 0.12% from 50 mm to 2 m, and we chose to agree with EPANET, because EPANET is what our users will check us against.
• The interface is inspired by and informed by EPANET’s. Its curve editor and its table of assets are where ours came from, and its five map colors are in our palette unsoftened, though our default is Viridis. What we added on top is the “++”: scenarios, world map and coordinate systems, import and export formats, fire flow, customers, custom properties, asset libraries you can import across projects, spreadsheet tables, find and replace, flexible multi-labels, a menu system we hope is easier, and being a web page rather than a Windows program.

That is a debt and a lineage. If EPANET had not existed, or had not been given away, this project would not exist.

2. Two solvers, and the newer one has less mileage

EPANET first appeared in 1993 and is used worldwide. Our built-in solver is new. It has been matched against EPANET’s answers on the examples we ship, and it has its record is no longer than that. If a result matters, run it under both engine settings and compare. If they disagree, please send us the network file.

3. We are new, with all that implies

Development started on 28 July 2026.

We do not publish a completeness claim against EPANET, and nothing on this site should be read as one. The “++” names what we added, not a claim to everything EPANET does. If you find something EPANET does that EPANET++ does not, please let us know.

4. Nobody has vetted this on your behalf

No EPA affiliation, no government affiliation, no university affiliation, no sponsor, no foundation, and no funding. Nobody has vetted this software on your behalf. Every claim on this page is one you can check yourself: they are set out one by one, each with its source, on the Citations page.

5. This is AI-assisted, and here is the reason

The software and this website are written with heavy use of AI. Tom Haws asked that his own statement of why be carried as he wrote it:

This would not be possible without AI. Tom Haws decided in 2026 that if AI is going to destroy the world, he better not use it for cat videos. His only justification for using AI is to tell the world the highest message of heaven: That they are loved and cherished forever, that they have nothing to fear, and that they are not ruining everything.

6. Our license is less free than EPANET's

Not public domain; less free than EPANET; less trusting than EPANET; arguably less collegial than EPANET. For better or for worse, we are currently working under Richard M. Stallman’s GNU General Public License 3.0, which is aggressively restrictive against locking up this work. The rationale is that this protects us all against property hoarders. Talk to us about this if you see the error of our ways.

EPANET carries no license at all, because a work of the United States government has no copyright to license. Anybody may take it and do anything, including take it private. We chose a license that forbids that, which is a restriction we impose and EPA did not. Reasonable people disagree about whether that is generosity or distrust. If you think we got it wrong, write to us.