We describe the supply and we certify nothing. Whether to drink from a given tap is a public-health judgement that belongs to the utility supplying it and to the authorities regulating it, not to a travel page. What this page can usefully do is tell you what kind of system you are drinking from and where the published analyses live.
Athens: mountain water, and a long aqueduct
Athens is supplied by EYDAP, and the water is not local. It is drawn from a system of mountain catchments and reservoirs, principally Lake Marathon in Attica, the Mornos reservoir in central Greece and the Evinos river system to the west, and brought to the city by aqueduct.
It is treated through a conventional full chain: coagulation, flocculation, sedimentation, filtration and disinfection, to European standards.
EYDAP publishes its analyses. If you want an answer about Athens tap water, that is where the answer is, and it is a better source than any page including this one.
The islands: two completely different situations
This is where the generalisations break down, and it is the useful part of this page.
Islands with real freshwater. The larger and wetter ones, including Crete, Corfu and Rhodes, have springs, rivers or aquifers and a conventional municipal supply drawn from them. The situation there resembles a mainland town.
Islands that make their water. Much of the Cyclades and many small Dodecanese islands have very little fresh groundwater and depend on desalination, typically reverse osmosis, and in some cases on water shipped in by tanker. Santorini, Mykonos, Milos and Ios are among the well-known examples.
Desalinated supply is treated water and it is regulated. It is also mineral-depleted, heavily disinfected and noticeably brackish or flat to taste, which is why the near-universal local habit on those islands is to drink bottled water regardless of what the analyses say.
That habit is the practical signal most visitors actually follow, and it is worth understanding as a taste and preference matter rather than reading it as a verdict.
What this means in practice
In Athens and Thessaloniki, tap water is ordinary municipal supply from a large regulated utility with published data.
On the big green islands, likewise, though supply arrangements vary by municipality rather than by island.
On the small dry islands, expect desalinated water, expect it to taste of very little, and expect everyone around you to be buying bottles. If you are trying to avoid plastic, a filter bottle addresses taste rather than anything else, and refilling from a tap on a desalinating island is a personal call.
Anywhere, if a property tells you not to drink from the tap, take that at face value. Local knowledge about a specific building’s plumbing beats any national generalisation.
The other water question: whether there is any
Worth raising because it matters more than taste. Small Greek islands run on limited water in high summer, and pressure and supply can be intermittent in August on the driest of them.
Power, water and wifi covers the practical side of that, including the plumbing convention that surprises visitors most.
Where this leaves you
Athens draws mountain water through a full treatment chain and EYDAP publishes the analyses. The big green islands have conventional supplies. The small dry ones make their water from the sea, which changes how it tastes and is why locals buy bottled. Read the utility’s own data rather than a travel page if you want a judgement, and take a property’s own advice about its own tap.
Quick answers
Where does Athens tap water come from?
From mountain catchments well outside the city, principally Lake Marathon in Attica, the Mornos reservoir in central Greece and the Evinos system to the west, brought in by aqueduct and treated by EYDAP through a full conventional chain to European standards.
Why does island tap water taste different?
Because on many small Greek islands it is desalinated seawater rather than groundwater. Reverse osmosis produces water that is mineral-depleted and heavily disinfected, which most people find flat or slightly brackish, and that taste is why bottled water is the local habit there.
Which Greek islands rely on desalination?
Much of the Cyclades and many smaller Dodecanese islands, including well-known cases such as Santorini, Mykonos, Milos and Ios. The larger, wetter islands such as Crete, Corfu and Rhodes have natural freshwater sources instead.
Should you drink the tap water in Greece?
That is a judgement for the utility supplying it and the authorities regulating it rather than for a travel page. What we can say is what kind of system you are on, that EYDAP publishes analyses for Athens, and that if a property tells you not to drink from its tap you should take that seriously.