Arsenic in water is not pollution. In Greece it comes out of the ground.

Most water contaminants have a culprit. Nitrate comes from fertiliser, lead from plumbing, PFAS from industry. Arsenic is different, and the difference matters for what you do about it: in most of the world where it is a problem, including Greece, it is not something anyone spilled. It is in the rock.

Arsenic occurs naturally in the earth’s crust. Where groundwater moves through certain geology — volcanic and geothermal formations especially — it dissolves arsenic and carries it into the aquifers that wells and boreholes draw from. This is why the worst arsenic crises in the world, in Bangladesh and West Bengal, arrived through wells dug to escape bacterial contamination in surface water. The wells solved the cholera problem and created a slower one.

The health case is not in dispute. The International Agency for Research on Cancer classifies arsenic and inorganic arsenic compounds as Group 1 — carcinogenic to humans, the same category as tobacco smoke and asbestos, and one of the few where the evidence comes directly from human populations rather than by inference. Long-term exposure through drinking water is associated with cancers of the bladder, lung, skin, kidney and liver, along with skin lesions and cardiovascular and developmental effects. The World Health Organization, the EU and the US EPA all set the same drinking water limit: 10 micrograms per litre.

What makes arsenic genuinely insidious is that there is nothing to notice. It has no taste, no smell, no colour, and it causes no immediate symptoms. Exposure is measured in decades, and by the time there is anything to see, the exposure has already happened. Nobody has ever detected arsenic in their water by drinking it.

Greece has real arsenic geology, and it is worth being specific rather than vague, because vagueness here helps nobody.

The published surveys identify affected areas in Chalkidiki, the Thessaloniki basin, eastern Thessaly and Lesvos. The concentrations in geothermal groundwater can be extraordinary — studies in the geothermal area of Chalkidiki have recorded values above 1,000 micrograms per litre in groundwater, a hundred times the drinking water limit, and in Thessaly concentrations up to around 130 micrograms per litre have been recorded, with the origin traced to the parent rock rather than to any human activity. One survey of wells in the Chalkidiki area found the majority exceeding the 10 microgram limit.

Two things must be said immediately alongside that, or the picture is false.

The first is that groundwater is not tap water. Those measurements are of aquifers, wells and irrigation water. Municipal supply in affected areas is treated, and Greece has built full-scale arsenic removal plants precisely because this problem is known. A high figure in a borehole in Nea Triglia is not a statement about what comes out of a tap in Thessaloniki.

The second is that the risk therefore concentrates exactly where treatment does not reach: private boreholes, older independent supplies, small settlements outside a municipal network, and buildings that draw their own water. If your water comes from a municipal supply, it is being tested for arsenic and treated if needed. If it comes from a borehole on the property, nobody is testing it unless you do.

The practical guidance follows from the chemistry, and one part of it catches people out. Boiling does not remove arsenic — it concentrates it, exactly as with nitrate and lead, because the water leaves and the arsenic stays. Standard carbon filters do very little. What works is reverse osmosis, or adsorption media designed for arsenic, or ion exchange. And the removal rate depends on which chemical form the arsenic is in, which is a laboratory question rather than a shopping one.

That is precisely why the Foundation will not fund an installation on a guess. Before a system goes into a children’s home, somebody has to know what is actually in that building’s water — because a filter chosen for the wrong contaminant does not just fail, it reassures everyone into not asking again. When our partner NearonYdor had its Twin system tested at the Chemistry Department of the National and Kapodistrian University of Athens, arsenic was among the eight metals in the panel, and it was below the limit of detection after filtration. We would rather show that than assert it.

The reason we write about arsenic at all, given that Greek municipal water is generally well managed, is that the buildings we serve are not always on the map. A children’s home in a small settlement, an older facility with its own supply, a shelter nobody has surveyed — these are the addresses where a national statistic stops being reassuring.

Sources: International Agency for Research on Cancer, Monographs — arsenic and inorganic arsenic compounds (Group 1); World Health Organization guidelines for drinking-water quality; published surveys of arsenic in Greek ground, thermal and tap waters, including studies of Chalkidiki, Thessaly and Lesvos; laboratory report, National and Kapodistrian University of Athens (Chemistry Department).