Ancient water structures serving as mills, water lifting machines and constructions such as aqueduct channels, cisterns and baths can be studied from their archeological remains, which normally give information on their construction method, maintenance, renovation and ultimate destruction. It is normally more difficult however, to obtain information on their functioning and the history of their use. Thankfully, many water systems used carbonate enriched groundwater, with dissolved calcium and high CO2 content, a result of passage of the water through soils and carbonate rocks. Such water can deposit carbonate on the walls of water systems, and even on the wood of water mills, gutters and machines for lifting water. The crystal structure and composition of carbonates in terms of stable isotopes of O and C, and trace elements depends on many factors such as the water composition, temperature, flow speed and biological content. The shape and height of deposits on the walls of water structures show water depth and its change with time. Detailed analysis of the crystal structure and composition of such carbonate deposits, in combination with a field survey and collected water samples from the original water sources can help to reconstruct the history of water flow in the system, and can provide new insight into technical details of the water structure, palaeohydrology of the sources, the use of the subject system and may record earthquakes or other natural hazards and possibly deforestation and other changes in vegetation by human impact.
Recent work on carbonates from water technologies are mostly focussed on Roman aqueducts due to their continuous use but recently, our group has started work on Roman mills, water machines and Roman baths to find meaningful correlations. In Barbegal, France, a complex of 16 linked watermills for flour production constituted one of the first industrial complexes in classical antiquity. Carbonates formed on the wood of the mills and millraces, and we are presently studying this material with the aim to reconstruct the structure of the mill and its history of use, and changes in the water quantity and quality in the mill system through its function. This can ultimately be a tool to understand aspects of ancient Roman economy by investigating unconformities as marks of maintenance periods. First results show that we can resolve stages in the construction and repair of the woodwork and establish how the machine was renovated during its use.
Before the construction of aqueducts, many established Roman baths where carbonate incrustations formed used groundwater that was lifted with the use of a bucket chain or other types of water-lifting mechanisms. We are presently studying this type of deposits in a Roman bath from Ampurias, Spain and Pompeii, Italy. Groundwater in Ampurias and in the Republican Baths of Pompeii was lifted from a well and deposited carbonate in a shallow bath that may have been used for heating. The deposits are different from those in Roman aqueducts and mills: they are similar in their internal structure, but with numerous unconformities and fine lamination, probably as a consequence of high evaporation. Moreover, the laminae possibly indicate fill-cycles of the baths. Analyses of these deposits can give information on the provenance of water used for baths, on intervals of bath use, on water quality and composition, and possibly on microbiological aspects.