"Επίσης, θέλω ένα ποτήρι νερό."

[Dmatafonov]

Also, I want one glass of water - why is that wrong?

[troll1995]

Added, thanks!

[GiEmmePi]

"a" glass of water should also be right ;)

[mizinamo]

It's best to post the whole sentence you tried, as there are many options accepted for this, most of which accept "a glass of water" as well.

[GiEmmePi]

ok, I understand

[MissesCG]

Why is "ποτήρι" here cup? Isn't there another word in Greek for cup?

[Dimitra956826]

Κούπα is the direct translation to cup. I guess the original creator had in mind that sometimes, κούπα and ποτήρι are interchangeable. I see your point though. We might keep these two seperate in the new tree. ^.^