Free public beta

Stormwater and sewer models with no pipe limits

Rillwork runs EPA's own SWMM 5 engine in your browser, on your computer. Open your .inp file, edit the network, run it, and print a drainage report your reviewer will recognise.

Try it now, free Join the beta list

Free during the beta. Planned price after the beta: $490 per user per year, whatever the size of the model. No account and no payment details needed to try it.

What it does

Rillwork is the editor, results viewer and report around EPA SWMM 5.2.4. It is a beta: the core works today, and we want to hear what has to work on day one for you.

Open and save SWMM 5 `.inp` files

Lines you did not edit are saved back byte for byte, comments and unknown sections included. Checked on all 73 models in EPA's example and regression suite.

Run EPA's unmodified engine

EPA SWMM 5.2.4, compiled to WebAssembly from EPA's own C source, with no changes. The run happens in your browser tab.

Edit the network

Junctions, conduits, outfalls, storage units, subcatchments and rain gauges. Select, move, add and delete, edit every property, undo and redo.

See the results

Colour nodes by depth, head or flooding and links by flow, velocity or capacity. Time slider, time-series plots, hydraulic grade line profiles and EPA's summary tables.

Print a drainage report

Print or save as PDF: EPA's summary tables, continuity errors, a network plan, your profiles and charts, and the engine version that produced them.

Design storms

Write an NRCS (SCS) Type I, IA, II or III 24-hour storm as a SWMM time series and point your rain gauges at it. The depth is conserved exactly.

Open exported models New, untested

Opens SWMM 5 .inp files exported from Civil 3D Storm and Sanitary Analysis and from SewerGEMS and CivilStorm. This import is new and has not yet been tested against real exports; it lists every change it makes. A sample file helps us most.

Any model size

No pipe, node or subcatchment limits in the software. The largest model in our own checks so far has 3,000 junctions.

Nothing to install

Runs in a modern desktop browser on Windows, Mac or Linux. Tested so far in Chromium-based browsers (Chrome, Edge).

Rillwork showing EPA's Example 1 after a run: the pipe network drawn over its subcatchments, pipes coloured by how full they are, the properties of the selected conduit on the right and EPA's summary tables below. — Results of a run on EPA's Example 1: links coloured by capacity, nodes by depth, the summary tables below. Real screenshot from the beta.

Hydraulic grade line profile between two nodes, ready to add to the report.

Editing a conduit: the selected pipe is highlighted on the network and its fields are open in the properties panel. — Edit any object; the saved file changes only the lines you touched.

The network editor with EPA's Example 1 open: the object list on the left, the network in the middle and the toolbar along the top. — Open a model and the whole network is drawn in its own coordinates.

The printable drainage report view, with the engine statement and summary tables. — The drainage report, printed from the browser or saved as PDF.

Your models stay on your machine

No upload. Your .inp files, data files and results are read and written in your browser. They are never sent to us or to anyone else.
No server doing the work. This site only delivers the app's files. The SWMM engine then runs inside your browser tab, on your own processor.
No other connections. The app's content security policy only lets it fetch its own files, and our checks run it with every other site blocked.
No account, no cloud credits. Open the app and start. You save your model as an ordinary SWMM 5 .inp file wherever you keep your project files.
Your files outlive the beta. Everything you save is standard SWMM 5 input, which opens in EPA's own program and other SWMM 5 tools.

The sign-up form on this page sends only what you choose to send, to Rillwork's own Cloudflare database. It uses Cloudflare Turnstile to keep out bots. The app itself loads neither.

Illustration: a laptop showing a drainage network, inside a protective boundary that a cloud's dotted line does not reach.

The engine is EPA SWMM 5.2.4

Rillwork does not have its own hydraulic engine. It runs EPA SWMM 5.2.4, the US Environmental Protection Agency's Storm Water Management Model, which is public domain. We compile EPA's C source to WebAssembly without changing it.

Results match EPA's engine. All 73 models in EPA's example and regression suite give the same results in Rillwork as a native build of the same source. Against EPA's own Windows build, the only differences are tiny rounding differences in the maths library, the same size as the spread between EPA's own Windows build settings.

73 / 73EPA test models pass

5.2.4EPA SWMM version, stated in every report

How we checked the engine

Questions

Is this a new hydraulic engine?

No. It runs EPA SWMM 5.2.4, which is public domain. Rillwork is the editor, viewer and report around it. See how we checked that the results match EPA's engine.

Is it really free?

Yes, during the beta. The planned price after the beta is $490 per user per year, with no pipe, node or subcatchment limits. We don't ask for payment details, so nothing can be charged automatically. Beta users will hear about pricing well before the beta ends.

Will reviewers accept the results?

The results come from EPA's own engine, and the report states which engine version produced them. Whether a submission is accepted is up to your reviewer, and the engineering judgement stays yours: please check results as you would with any tool.

Can I open models from Civil 3D or SewerGEMS?

Rillwork opens SWMM 5 .inp files, including those exported from Civil 3D Storm and Sanitary Analysis and from SewerGEMS and CivilStorm. The import path is new and has not yet been tested against real exports. It handles the publicly documented quirks and lists every change it makes. If an export doesn't open cleanly, a sample file (with anything sensitive removed) is the most useful thing you can send us.

Where are my models stored?

On your computer, where you save them. The app reads and writes files in your browser and uploads nothing. There is no Rillwork account and no cloud copy.

What happens to my work when the beta ends?

Your models are ordinary SWMM 5 .inp files on your own disk, so they keep working in any SWMM 5 tool, including EPA's own program.

What doesn't it do yet?

There are no map backgrounds yet (the network is drawn in the model's own coordinates), no GIS import, and no regional rainfall distributions beyond the four NRCS 24-hour types. It reads and writes SWMM 5 .inp files only. Tell us what you need first.

Which browsers does it work in?

A current desktop browser. We test in Chromium-based browsers (Chrome and Edge). If something doesn't work in yours, please tell us which one.

Who is building it?

An independent developer.