In Athens, the tap water is considered safe to drink. I have personally visited Athens multiple times and have never had any issues with drinking tap water there. The water is treated and meets the European Union standards for drinking water quality. However, it is always a good idea to confirm with the locals or hotel staff just to be sure.
One thing to keep in mind is that the taste of tap water can vary from place to place. Some people might find the taste of tap water in Athens to be slightly different from what they are used to. If you are not comfortable with the taste, you can always opt for bottled water, which is readily available and affordable in most places.
It is important to note that while tap water in Athens is safe to drink, the same cannot be said for all parts of Greece. In some smaller towns or rural areas, the tap water may not be potable. In these cases, it is best to ask the locals or rely on bottled water.
If you are traveling outside of Athens and plan to drink tap water, it is advisable to carry a reusable water bottle with you. This way, you can fill it up with tap water when it is safe to do so and reduce plastic waste by avoiding single-use plastic bottles.
To sum up, while tap water in Athens is generally safe to drink, it is always a good idea to check with the locals or hotel staff for confirmation. In other parts of Greece, it is better to rely on bottled water or ask about the safety of tap water.