QGIS

QGIS needs little introduction as a GIS; it earns its place in a water-engineering directory because it has quietly become the discipline's default spatial platform. Terrain processing via bundled GRASS, SAGA and GDAL providers; mesh-layer support that reads TUFLOW, Telemac and Delft3D results natively; profile and cross-section tooling; and a plugin ecosystem covering everything from watershed delineation to EPANET network building.

For a water team, QGIS plus a handful of plugins replaces a five-figure GIS licence for the majority of drainage, floodplain and catchment workflows — and its Python console (PyQGIS) makes those workflows scriptable end to end.