Nitrates in Greek tap water: what the numbers actually mean

If you have read anything about nitrates in Greek drinking water, you have probably seen two numbers: 50 milligrams per litre, and 10. The usual telling is that 50 is the lax legal limit and 10 is what the careful countries use. It is repeated constantly, including — until today — on this website.

It is wrong, and it is worth taking a minute to explain why, because the mistake makes a real problem sound like a scandal and a safe measurement sound alarming.

The two numbers are not in the same units. The European limit of 50 mg/L measures nitrate itself. The United States limit of 10 mg/L measures only the nitrogen inside the nitrate. Nitrate weighs about 4.43 times what its nitrogen does, so 10 mg/L of nitrate-nitrogen is roughly 44 mg/L of nitrate. The American standard and the European standard are, to within a rounding error, the same standard. Neither country is being lax, and a Greek tap measuring 12 mg/L of nitrate is not five times over an American limit — it is comfortably under it.

So where does the real concern sit? Both limits exist for one specific reason, and it is not adults. They were set to protect bottle-fed babies from methaemoglobinaemia, sometimes called blue baby syndrome: nitrate interferes with the blood’s ability to carry oxygen, and an infant under six months has not yet developed the defences an adult has. That is why the World Health Organization describes its nitrate guideline as protective for bottle-fed infants first, and everyone else as a consequence.

Which means the number to watch is not an abstract legal threshold. It is the number coming out of the tap that a particular baby’s formula is being made with. A household that never mixes formula and a children’s home with infants in it are not facing the same question, even on identical water.

The second thing worth knowing is that nitrate is invisible. You cannot taste it, smell it or see it, and boiling makes it worse rather than better — the water evaporates and the nitrate stays, so the concentration rises. There is no home test you can do by eye. Somebody has to measure it.

Nitrate in drinking water comes overwhelmingly from agriculture: fertiliser and manure that rain washes off fields and down into the groundwater that municipal supplies draw from. This is why the problem in Greece is geographic rather than random. It concentrates in farming country and in the areas drawing on aquifers beneath farming country, and it barely registers in places supplied from protected surface reservoirs. Athens, drawing from the EYDAP network, generally measures very low. Agricultural plains do not.

Greek measurements are more available than people realise. Municipal water companies publish analyses, and the Association of Municipal Water Supply and Sewerage Companies collates them. Greek press investigations over recent years have found exceedances of the 50 mg/L legal limit in specific agricultural localities — not in city centres, but in villages and suburbs whose water comes from local boreholes. That is a serious finding, and it is also a narrow one. It is not a statement about Greek tap water in general.

What should a family or a children’s home actually do with this?

Start by finding the published analysis for your own supply, from your local water company rather than from a national average. If there are infants in the building, that is not an academic exercise. If the figure is near or above 50 mg/L as nitrate, do not use it for formula, and do not boil it in the hope of fixing it.

And know what does and does not remove nitrate. Most filter jugs and most carbon filters do essentially nothing to it — nitrate is a small dissolved ion and carbon does not hold it. Reverse osmosis and ion exchange do remove it. When the Foundation funds a system for a children’s home, this is exactly why we insist on knowing what is in that building’s water first: fitting a filter that does not address the actual contaminant is worse than fitting nothing, because everyone then stops worrying.

That is the honest position. Greek drinking water is, in most places, well within the legal limits. In specific agricultural areas it is not, the people most at risk from that are infants, and the only way to know which situation you are in is to look at the measurement for your own tap.

Sources: the EU Drinking Water Directive (2020/2184) sets the 50 mg/L nitrate limit; the US Environmental Protection Agency sets 10 mg/L measured as nitrate-nitrogen; the World Health Organization’s nitrate guidance explains the infant basis for both.