Hydraulic & Process Simulation

Free, public-domain stormwater, wastewater, and combined sewer system simulation model by the US Environmental Protection Agency -- dynamic hydrology-hydraulic-water quality simulation for single-event or continuous modeling of rainfall-runoff, pipe/channel routing, green infrastructure/LID controls, and pollutant loads; the industry-standard computational engine used worldwide for drainage design, CSO/SSO mitigation, floodplain mapping, and regulatory compliance (NPDES, CMOM, TMDL).

Solid -- the free, public-domain industry-standard computational engine for stormwater/wastewater drainage modeling worldwide (FEMA-approved for NFIP studies), with an open-source C API and 50+ programmer toolkit functions enabling deep customization and integration; no subscription cost, a large active community (open SWMM, GitHub USEPA repo), and FEMA approval make it the de facto baseline for water infrastructure modeling; scoring reflects its outstanding value and openness despite a dated Windows-native GUI, no vendor support contract, and desktop-only delivery (no REST/CLI).

Free, public-domain water distribution system modeling software by the US Environmental Protection Agency -- performs extended-period simulation of hydraulic and water-quality behavior within pressurized pipe networks (pipes, pumps, valves, tanks), tracking flow, pressure, water age, chlorine residuals, and contaminant transport; provides a C Programmer's Toolkit (DLL with 50+ functions) for custom integration; the industry-standard computational engine underlying most commercial water-distribution modeling packages worldwide.

Solid -- the free, public-domain industry-standard computational engine for water distribution modeling worldwide, with a C Programmer's Toolkit API enabling deep customization and integration into GIS/CAD environments; no subscription cost, an active open-source community on GitHub, and the .inp format as the de facto industry interchange standard make it the baseline for water distribution analysis; scoring reflects outstanding value and openness offset by a dated Windows-native GUI, no vendor support contract, and desktop-only delivery (no REST/CLI).

Advanced stormwater, wastewater, watershed, and water distribution modeling software by Computational Hydraulics International (CHI) -- built on the EPA SWMM5 engine with a powerful GIS interface, 1D/2D hydraulic modeling, intelligent scenario management, model calibration tools, and green infrastructure/LID design; used worldwide by engineering consultants, municipalities, and utilities for drainage design, floodplain mapping, CSO/SSO analysis, and water quality modeling.

Solid -- the premier commercial front-end for EPA SWMM5 with transparent pricing ($1,600-2,400/yr per seat), a 30-day free trial, and an intuitive GIS interface that dramatically lowers the learning curve vs raw SWMM; unlimited model size, industry-leading technical support, and strong community/ecosystem (OpenSWMM, CHI journal, annual conference); no REST/CLI agent access and Windows-only desktop delivery cap agent-driven workflows, but for human-led drainage and stormwater modeling it is the clear commercial value leader.

Integrated catchment modeling software for stormwater, wastewater, and flood network analysis -- 1D/2D hydraulic and hydrologic simulation, cloud or local compute, collaborative scenario management, and rule-based network design for sewer and stormwater engineers at utilities and engineering consultancies.

Situational -- powerful integrated 1D/2D hydraulic modeling with cloud compute scaling, Ruby scripting, and collaborative simulation across stormwater/wastewater/flood workflows, but quote-only pricing (no public price tier) and a steep learning curve for hydraulic modeling specialists limit accessibility for smaller teams.

Water distribution system modeling and management software built on ArcGIS Pro -- provides hydraulic analysis, criticality analysis, pressure transient modeling, leakage detection, fire flow analysis, and what-if scenario simulation for water utilities and engineering firms planning, designing, and operating water distribution networks with spatial analysis and GIS integration.

Situational -- industry-standard water distribution modeling with deep ArcGIS Pro integration, fire flow and criticality analysis, and Ruby scripting for automation; quote-only pricing (no public price tier, RF1) and desktop-only delivery with no standalone REST API limit value for teams not already on Autodesk/ArcGIS infrastructure.

Wastewater treatment plant modeling and simulation software by Hydromantis (a Hatch company) -- the first commercially released dynamic wastewater treatment plant simulator, providing a drag-and-drop interface with the industry's largest library of unit process models (Mantis2 biological model, carbon/nitrogen/phosphorous removal, sulfur/selenium, GHG carbon footprint) for designing, optimizing, and managing municipal and industrial wastewater treatment plants; includes steady-state and dynamic simulation, sensitivity analysis, process optimization, scenario management, and Python scripting (Pro+ tier).

Situational -- the established wastewater treatment plant simulation leader (since the 1990s) with transparent annual pricing ($3,700-10,400/yr), the industry's largest unit-process library, and Python scripting integration at the Pro+ tier; steep learning curve, Windows-only desktop delivery with no REST API/CLI (RF2), and niche applicability to wastewater process engineers limit broader adoption.

Water distribution system modeling and simulation software for hydraulic analysis, water quality modeling, fire flow analysis, energy management, and pipe network calibration -- part of Bentley's OpenFlows portfolio, serving municipal water utilities and engineering consultants.

Situational -- industry-standard water distribution modeling with Bentley iTwin Platform integration and OpenFlows ecosystem, but quote-only pricing (RF1) and proprietary-format lock-in within the Bentley ecosystem limit value for teams not already on Bentley infrastructure.