WaterGEMS vs EPANET: What the Licence Adds

WaterGEMS and EPANET compute the same hydraulics. Bentley's own help says the core numerical analysis in WaterGEMS and WaterCAD is based on EPANET, the engine developed by the US EPA. What the licence buys is the work around the solve: building the model from GIS and CAD data, calibrating it, optimising pipe sizes and pump schedules, testing fire flow and pipe outages, and keeping many scenarios in one model. Whether that is worth paying for depends on how much of that work you do.

What is the difference between WaterGEMS and EPANET?

EPANET is a free, public domain solver for hydraulics and water quality with a plain Windows interface; WaterGEMS is a commercial modelling environment from Bentley built on an enhanced version of the same engine. EPANET gives you the simulation. WaterGEMS adds GIS and CAD integration, the Darwin optimisation tools, fire flow and criticality analysis, a scenario manager, SCADA data, and a direct route into Bentley's HAMMER for transients. For a pressure check on a small network the two give the same answer. For a utility model maintained over years, they are different kinds of product.

Is WaterGEMS based on EPANET?

Yes. The default WaterGEMS solver is EPANET with Bentley's own improvements and bug fixes, so Bentley says small differences from EPANET results are expected. New models default to a Bentley engine based on EPANET 2.2. An Engine Compatibility option runs the model in a pure EPANET 2.00.10, 2.00.12 or 2.2 mode instead, which switches Bentley's changes off so the results match that EPANET release. Imported EPANET models default to the matching EPANET mode.

This matters in review. If a consultant delivers a WaterGEMS model and the client checks it in EPANET, set the compatibility mode first, or the two will disagree slightly and nobody will know why.

What does EPANET do for free?

EPANET runs extended period simulations of hydraulics and water quality in pressurised pipe networks, and the EPA states there is no limit on network size. It handles pressure dependent demands, tank level, timer and rule based controls, constant and variable speed pumps, valves, pumping energy and cost, and the Hazen-Williams, Darcy-Weisbach and Chezy-Manning headloss formulas. For water quality it models water age, source tracing, and reacting substances such as chlorine with bulk and pipe wall reactions. It is public domain and can be copied and distributed freely.

The EPA's desktop release is EPANET 2.2, from 2020. Development continues in the open source project on GitHub, where EPANET 2.3 added a FAVAD model for pressure dependent leakage, a positional control valve and a flow balance report. Free tools have grown around the engine: WNTR, from the EPA and Sandia, runs pipe, pump, segment and fire flow criticality studies in Python. Paid tools have too: PipePilot, which is ours, runs EPANET 2.3 in a browser by subscription at geopilotai.com/pipepilot.

What the EPANET program itself lacks is the tooling. It holds one set of data at a time; scenario files of demands, roughness and controls can be exported and read back in, but there is no manager to compare them. There is no GIS link in the desktop program, no optimisation and no transient solver. Each gap can be filled with code against the toolkit, which is how much research is done, but then the code is yours to maintain.

What does WaterGEMS add on top of EPANET?

• GIS and CAD integration. Bentley lists WaterGEMS as running stand-alone or inside ArcGIS Pro, MicroStation and AutoCAD, with one project data source shared by all of them. Inside ArcGIS Pro the model is edited in the GIS with no import or export step. The host program needs its own licence.
• Darwin Calibrator. A genetic algorithm search for the pipe roughness, junction demands and link status that best match measured pressures and flows.
• Darwin Designer. Optimised pipe sizing and rehabilitation plans, set against unit costs and pressure and velocity limits.
• Darwin Scheduler. Pump schedules optimised for energy cost in extended period runs.
• Fire flow and criticality. Fire flow analysis checks what each hydrant can deliver while pressures stay above the limits you set, across the network in one run. Criticality analysis finds the segments between valves, shuts each one in turn, and reports the demand shortfall each outage causes.
• Scenario management. Many what-if scenarios, built from alternative demands, physical data and controls, held in one model and compared side by side.
• Transients through HAMMER. WaterGEMS does not solve water hammer itself. HAMMER, Bentley's transient program, opens WaterCAD and WaterGEMS models directly; you add wave speeds, the transient event and surge protection there.
• SCADA data. Live SCADA signals can feed the model. Bentley's operational product built on this is WaterSight, covered in digital twin software for water utilities compared.

What is the difference between WaterCAD and WaterGEMS?

WaterCAD is the smaller product, and Bentley now sells it, WaterGEMS and HAMMER as tiers of one subscription called OpenFlows Water. As listed on Bentley's product page in October 2026, Essentials is WaterCAD for up to 100 pipes; Standard adds HAMMER, for up to 1,000 pipes; Advanced adds WaterGEMS, for up to 5,000 pipes; Ultimate has no pipe limit. Fire flow, criticality, scenario comparison and CAD and GIS integration are listed from the lowest tier. AI assisted calibration, pipe sizing and rehabilitation optimisation, pump scheduling and SCADA integration appear only in Advanced and Ultimate, the tiers that include WaterGEMS.

Every tier is a 12 month Virtuoso subscription. Bentley shows starting prices by region without a date, so check the page for your country before budgeting. Students and educators get free access.

Can you move a model between WaterGEMS and EPANET?

Yes, through the EPANET .inp file. WaterGEMS imports and exports .inp files, but because EPANET has no scenarios, only the active scenario goes out. The network and its data survive the trip; the scenario structure, Darwin setups and GIS links do not. Moving the other way is simpler, since an EPANET model is a subset of what WaterGEMS holds.

When is EPANET enough, and when is WaterGEMS worth it?

EPANET is enough when one modeller builds the model, the network is a scheme or a town rather than a city, and the deliverable is a report. It is enough for research and teaching, and for any team that would rather script calibration or criticality in Python with WNTR than pay for it. Many design checks need nothing more.

WaterGEMS earns its subscription when the model lives in GIS and has to stay in step with it, when you calibrate and size pipes often enough that manual trial and error costs more than the tier, when fire flow and criticality reports are a routine client requirement, or when you also need transients in the same model family. A consultant whose client already holds a WaterGEMS model rarely has a choice, because extending the client's model is cheaper than rebuilding it.

If the alternative on the table is Autodesk rather than EPANET, see InfoWorks WS Pro vs InfoWorks ICM and InfoWorks alternatives for small teams. The wider field is in water network design software compared, and if the network carries stormwater rather than supply, start with EPANET vs SWMM.

Smart Bhujal builds and calibrates network models in EPANET and WaterGEMS and resells none of these packages; the work is set out on our water distribution modeling page.