Simple, often artificial problems are normally preferred for introductory lab courses and are restricted to indoor participation. Microtitrations make it possible to leave the lab and study water chemistry directly in the natural environment. An exemplary outdoor challenge is presented here: travertine formation is context-rich, has to be examined on site, fits very well into a beginner's curriculum, and imparts multidisciplinary knowledge. The method is transferable to other water chemistry projects. Experiences with homemade water hardness kits during ten student fieldtrips to travertine forming Waterfall Dreimühlen (Eifel, Germany) are shared, along with a corresponding Bachelor's project.