νερό, Nero
Greek in Greek is spelled ellenika and written ελληνικά.
You use the Greek alphabet.
From Koine (Common) Greek, "water" is transliterated as "hydor" (prounounced HOO-dor, spelled "upsilon [rough breathing] delta omicron rho"). This comes into English properly as the prefix "hydro-",...
Τι [Tee]