Completed in 1957, the new buvette (pump room) of the Source Cachat in Evian-les-Bains is to be classed among twentieth-century icons. The building was the outcome of a fruitful partnership be-tween an experienced architect, Maurice Novarina, an “inspired constructor”, Jean Prouvé, and an architect-engineer, Serge Ketoff, who was capable of combining a highly expressive sensibility with rigorous structural calculations. The result of this collective adventure was a “technical object” of outstanding value. The Evian buvette is indeed a bravura piece, a tour de force brilliantly carried off, and goes far beyond the showcasing of industrial materials. “Precision mechanics” rather than simple “Meccano”, the building is a perfectly calibrated assembly of highly divers elements and components, in accordance with a relationship of true interdependence that takes advantage of this tensioning. The very nature of this “ordered system” entails an equally rigorous approach to restoration. The logic of the interlocking of the constructional elements then becomes the unifying thread of any in-tervention aimed at preserving the building, today a listed monument. This major work was also an opportunity to resituate the Evian “Buvette” in the current state of Jean Prouvé's oeuvre with respect to its preservation, which raises major ethical issues – sometimes para-doxical, often problematic – which go far beyond the simple technical constraint. Between reassem-bly, reconstruction or restoration, the approaches adopted in recent years have been highly diverse, not to mention the multitude of buildings that have been dismantled, dismembered, restored and then auctioned off as design pieces. This exceptional corpus, through a survey coherent with its current state, yields multiple reflections on the heritage of the twentieth century and its preservation.