Is SWMM, MODFLOW, HEC-RAS or TUFLOW Free?

Each answer below says yes or no first, then names the licence and what "free" covers. Every fact was read from the developer's own pages on 17 October 2026. Licence terms change, so check the linked page before a project or a course depends on one. For the broader question of what a paid licence buys over a free solver, see open source vs commercial water modelling.

Is EPA SWMM free?

Yes. The US Environmental Protection Agency describes the Storm Water Management Model as "open source, publicly, and freely available software for use worldwide", and the source code in EPA's GitHub repository is released into the public domain. Free covers the Windows program with its interface, the computational engine, and the right to use and build on the code, for commercial work as well as research. The newest installer on EPA's SWMM page is SWMM 5.2.4.

Where the bare program slows a large study down is covered in PCSWMM vs EPA SWMM.

Is SWMM free?

Yes, if you mean EPA SWMM, which is the program most people mean by SWMM. The confusion comes from commercial packages that run the SWMM engine inside their own interface. PCSWMM from CHI is the best known, and XPSWMM grew from the same lineage. Those products are licensed and sold separately. The engine inside them stays free; what you pay for is the environment around it. Stormwater modeling software compared sets out what each of them adds.

Is PCSWMM free?

No. PCSWMM is commercial software from CHI and professional use needs a paid licence. Two routes into it cost nothing.

• A 30-day trial. CHI offers a 30-day trial of the full PCSWMM Professional 2D, issued once your details have been verified.
• The CHI educational grant. Anyone affiliated with an educational institution is directed to the grant instead of the trial. CHI describes it as "easy, free access to a PCSWMM subscription" for post-secondary undergraduate and graduate students, faculty and researchers, for teaching and research, renewable every 12 months.

The grant comes with conditions, listed on CHI's grant page: a post-secondary email address and proof of affiliation, no commercial use, a citation of PCSWMM in any published paper, a copy of the research results and a short progress report sent to CHI, and no direct technical support. The full comparison with the free program is in PCSWMM vs EPA SWMM.

Is MODFLOW free?

Yes. MODFLOW 6, the current version from the US Geological Survey, is in the public domain in the United States, and its licence file waives copyright worldwide under the CC0 1.0 Universal dedication. Anyone may copy, modify and distribute it, including for commercial purposes, without asking permission. The latest approved USGS release is MODFLOW 6.8.1, published on 23 September 2026.

Free covers the model and its source code. Several graphical interfaces built around MODFLOW are separate commercial products with their own licences; USGS publishes its own interface, ModelMuse, which supports MODFLOW 6. How MODFLOW sits against the paid groundwater codes is covered in groundwater modelling software compared and FEFLOW vs MODFLOW.

Is TUFLOW free?

No. The TUFLOW manual states that "a TUFLOW licence is required to run TUFLOW", and BMT supplies licence quotes on request. Three things need no licence:

• The tutorials and example models. TUFLOW runs licence free on its own tutorial models, and the manual says there is no need to buy a licence to learn the software.
• Demo mode. Setting Demo Model == ON in the control file runs small test models on your own data without a licence, within limits: no more than 100,000 2D cells in the bounding rectangle, 30,000 active 2D cells, 100 1D channels, one 2D domain, and 10 minutes of simulation clock time.
• Third party software. A GIS, text editor or interface used to build the model does not need a TUFLOW licence.

For universities, the TUFLOW education guide points teaching and research to the free tutorials and demo mode, with a paid licence for unrestricted use. For how TUFLOW compares with the other flood models, see flood modelling software compared and InfoWorks ICM vs TUFLOW.

Is HEC-RAS free?

Yes in cost, though it is not open source. The HEC-RAS download page says use is not restricted and individuals outside the US Army Corps of Engineers may use the program without charge. The current release listed there is HEC-RAS 7.0.1, with HEC-RAS 2025 offered as a beta.

Two limits sit behind "free". HEC's terms and conditions say the software may not be modified, decompiled or reverse engineered, and copies remain the property of HEC. HEC also does not support users outside the Corps: it points them to its public Discourse forum and to commercial vendors. Where HEC-RAS fits against the paid river models is in HEC-RAS vs MIKE, and against SWMM in SWMM vs HEC-RAS.

Is EPANET free?

Yes. EPA's EPANET page says "EPANET is public domain software that can be freely copied and distributed." EPA's EPANET 2.2 source repository is released under the MIT licence, and continued development now happens in the OpenWaterAnalytics open source project, where the latest release at the time of checking was EPANET 2.3.5. The newest installer on EPA's own page is still EPANET 2.2. How it relates to SWMM is in EPANET vs SWMM, and the paid network design tools are in water network design software compared.

What is the best free drainage software?

EPA SWMM, for most urban drainage work. It is free without conditions, it models rainfall runoff, pipe and channel hydraulics, storage and water quality, and and anyone reviewing the model can open it in the same free program. Where the question is river flooding or overland flow across terrain rather than the pipe network, HEC-RAS is the free choice. PCSWMM and TUFLOW are free only through trials, grants or a small demo mode.

We also sell two browser tools of our own, and they are not free: DrainPilot, which runs EPA SWMM 5.2.4, and PipePilot, which runs EPANET 2.3 for water supply networks. Both are paid subscriptions built on those free engines.

Summary table

Software	Free?	Licence	What free covers
EPA SWMM 5.2.4	Yes	Public domain (US EPA)	Program, engine and source, any use
PCSWMM	No	Commercial (CHI)	30-day trial; renewable educational grant for post-secondary teaching and research, no commercial use
MODFLOW 6.8.1	Yes	Public domain in the US, CC0 1.0 worldwide (USGS)	Model and source, including commercial use
TUFLOW	No	Commercial (BMT)	Tutorial and example models; demo mode up to 30,000 active 2D cells and 10 minutes of clock time
HEC-RAS 7.0.1	Yes, at no charge	HEC terms of use (US Army Corps of Engineers); not open source	Use without charge; no modification, no support outside the Corps
EPANET	Yes	Public domain (US EPA); source under MIT	Program, engine library and source

All entries were checked against the developer's own pages on 17 October 2026.

Smart Bhujal runs drainage studies in EPA SWMM, PCSWMM and InfoWorks ICM. If the free route does not fit the study, our stormwater and drainage modeling page sets out how we work.