The waters of the Palace of Versailles: secondary carbonate deposits in the famous fountains bear witness of their history. Case study on the origin of lead.

The issue of water resources is an old one, and echoes current concerns, with freshwater resources under increasing anthropogenic pressure. It encompasses aspects related to researching its origin, transport, use, and even its quantification and quality. The use of natural archives to trace the history of this resource in relation to environmental variations or anthropogenic activities is growing rapidly. Here we present a study of secondary carbonate concretions found in the water supply systems of the Palace of Versailles. The supply of water to the castle gardens presented a series of major technical challenges, which evolved considerably throughout its history. Formed layer by layer over time by water leaks, they represent unique archives of the waters of the past that allowed them to form. They therefore offer a unique opportunity to track changes in supply or even the influence of various modifications made over time.Here we present a study of concretions taken from under the famous Latone fountain, under the Neptune basin, and in a technical gallery. We discuss the chronological aspects for precise dating and the geochemical tracers to be monitored. We focus here on the study of lead, an element that is very present both in the materials used for fountains and water supply systems and as a marker of urban pollution. We use its isotopic signature to discuss its origin in these waters and its evolution over time.