GIS.lab (http://web.gislab.io) connects open source technologies together: QGIS is used as desktop environment as well as the server for data serving. A web client is based on OpenLayers and AngularJS libraries. On the server side, thin Django application is developed as well. Beside a core functionality like responsive web design, support for topics, base and overlay layers, legend, identification, attribute table data filtering, measurement, and print, which are mainly based on QGIS server, serving the data via OGC WMS and WFS, the GIS.lab infrastructure can provided support for additional functionality implemented as so-called plugins. This contribution is focused on the possibilities how to extend the GIS.lab Web infrastructure when dealing with OGC Web Processing Service (WPS). The process inputs and outputs definitions will be designed by the user (project administrator) in QGIS desktop environment, using GIS.Lab publishing plugin. A hydrological modeling, namely tool for reduction day precipitation to subday (GRASS module r.subdayprecip.design), will be used as demonstration of WPS integration into the GIS.lab Web infrastructure. Co-authors: Petr Kavka, Ludek Strouhal, Ivan Mincik, Marcel Dancak, Jachym Cepicky