Limescale deposits in wells, pipes, and bathing facilities provide information about Pompeii's ancient water supply

The city of Pompeii was buried by the eruption of Mount Vesuvius in AD 79. Researchers at Johannes Gutenberg University Mainz (JGU) have now reconstructed the city's water supply system based on carbonate deposits – particularly the transition from wells to an aqueduct. The results were published yesterday in the journal PNAS. "The baths were originally supplied by deep wells with water-lifting devices, and the hygienic conditions in them were far from ideal," says Dr. Gül Sürmelihindi from the Institute of Geosciences at JGU, first author of the publication. "Over time, however, the water-lifting devices were upgraded through technological developments before being replaced by an aqueduct in the first century AD, which provided more water and allowed more frequent refreshment of water for bathing."

Geochemical differences in the deposits provide a wealth of information

To reconstruct the ancient water supply, Sürmelihindi and her colleague Professor Cees Passchier used isotope analysis to examine carbonate deposits that had formed in various components of the city's water infrastructure – such as the aqueduct, water towers, well shafts, and the pools of the public baths. "We found completely different patterns of stable isotopes and trace elements in the carbonates from the aqueduct and in those from the wells," says Sürmelihindi. Based on these different geochemical characteristics, the team was able to determine the origin of the bathing water and draw conclusions about Pompeii's water management system and quality changes in provided water. They discovered that the wells tapped into highly mineralized groundwater from volcanic deposits, which was not ideal for drinking purposes. This agrees well with what was previously known: during the reign of Augustus, the aqueduct was built in Pompeii, significantly increasing the amount of available water for bathing and providing drinking water.

Water in the baths was contaminated

"In the so-called Republican Baths – the oldest public bathing facilities in the city, dating back to pre-Roman times around 130 BC – we were able to prove through isotope analysis that the bath water was provided from wells, and not renewed regularly. Therefore, the hygienic condition did not meet the high hygienic standards usually attributed to the Romans," explains Sürmelihindi. Probably, the water was only changed once daily, which, according to Sürmelihindi, would not be surprising: "After all, the baths were supplied by a water-lifting machine, powered by slaves via a kind of treadwheel."

The researchers also found lead, zinc, and copper peaks in the anthropogenic carbonate deposits which indicates contamination with heavy metals in water of the baths. This suggests that boilers and water pipes were replaced, which increased the heavy metal concentrations. An increase in stable oxygen isotopes also shows that the pools in the Republican Baths provided warmer water after the renovation.

Unusual, periodic patterns could indicate volcanic activity

The researchers also found peculiar, cyclic patterns in the carbon isotope ratio of carbonate from the wells. According to Passchier, a possible cause could lie in the fluctuating amount of volcanic carbon dioxide in the groundwater – this cyclicity may provide information on the activity of Mount Vesuvius long before the AD 79 eruption.