According to the study report recently published in PNAS, the research team reconstructed bathing conditions by analyzing carbonate deposits (the crusty “limescale” left behind by water) preserved in Pompeii’s hydraulic infrastructure. Those mineral layers captured changes in water source, maintenance, and even pollution, offering a surprisingly direct window into what bathers were sitting in.
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Carbonate samples from the so-called Republican Baths in Pompeii. (© Cees Passchier/PNAS)
What the Researchers Actually Tested
The study, led by geoscientists at Johannes Gutenberg University Mainz, sampled carbonate incrustations from wells, pools, and drainage channels at Pompeii, then compared them with carbonates from the city’s aqueduct and water towers. Their stable isotope and trace-element results separated “well-fed” water systems from “aqueduct-fed” systems very clearly.
One of the most striking findings came from the Republican Baths (among Pompeii’s oldest public baths, dating to around 130 BC). Here, the chemistry showed bathwater came from deep wells rather than an aqueduct, and the isotopic pattern indicated it was not regularly replenished reports Archaeology Magazine.
The authors report a sharp drop in carbon isotope values from the wells to the bathing pools, consistent with contamination by human waste. This implies bathers were contributing sweat, urine, and other organic matter to water that stayed in circulation longer than we might expect.
Frigidarium (cold room) at the Stabian Baths, Pompeii. (Miguel Hermoso Cuesta/CC BY-SA 4.0)
Heavy Metals, Renovations, and a Shift to “Better” Bathing
Alongside the waste signals, the mineral crusts also recorded elevated levels of lead, zinc, and copper in some bathhouse samples - evidence of heavy metals in the water system. In Pompeii’s baths, those metals appear to have increased during renovations, likely when boilers and pipes were replaced, which changed the plumbing materials interacting with the water.
The picture improves after Pompeii was connected to a Roman aqueduct in the 1st century AD. The study explains that aqueduct-fed water came from karst springs (generally less mineralized than volcanic groundwater) and, critically, enabled higher water volumes, making it easier to refresh pools more frequently.
BBC Science Focus, reporting on the same paper, notes that before the aqueduct, water was lifted up from wells using a machine and was likely replaced only about once a day. That limited turnover would have made “clean” bathing difficult even with attentive maintenance.
A Social “Spa” That Wasn’t Really About Hygiene
This is where the story becomes more human than chemical. The Roman baths mattered because they were social infrastructure - busy, noisy public spaces for exercise, meetings, and leisure. If the water sometimes lagged behind the ideal, many people likely tolerated it because the bathhouse offered far more than cleanliness.
In the Science Focus report, historian Alexander Meddings (not involved in the research) is quoted describing baths as grim by modern standards, with bathers “peeing in the pools” and scraping off dead skin, leaving a floating “layer of scum.” Those remarks align with the study’s central claim: the “high hygienic standards” often attributed to the Romans didn’t necessarily apply in early Pompeii.
The team is also conducting further DNA work on the carbonate deposits, which could provide more direct evidence of the biological material circulating through these systems.
Top image: Men’s entrance to the Stabian Baths (Stabian Baths complex, Pompeii).
Source: Mary Harrsch/CC BY-SA 4.0
By Gary Manners
References
Federico, C. 2002. Magma-derived gas influx and water-rock interactions in the volcanic aquifer of Mt. Vesuvius, Italy. Available at: https://www.pnas.org/doi/10.1073/pnas.2517276122
Sürmelihindi, G. & Passchier, C.W. 2026. Seeing Roman life through water: Exploring Pompeii’s public baths via carbonate deposits. Available at: https://www.pnas.org/doi/10.1073/pnas.2517276122
Viegas, J. 2026. Pompeii’s Water Quality Analyzed. Available at: https://archaeology.org/news/2026/01/15/pompeiis-water-quality-analyzed/
Williams, W. 2026. The ancient baths of Pompeii were full of lead and human waste, study finds. Available at: https://www.sciencefocus.com/news/pompeii-baths-disgusting-water
