I was under the impression that 'nero' and 'hydor' were both 'water' in Greek. But apparently I mixed up modern and ancient usage in my head. Oh, well...
We actually do use both in modern Greek, but "hydor" is mostly used in compound words.
In ancient (but also in modern) Greek, "nearon hydor" means "young (i.e. "fresh") water", and at least according to a greek professor whom I was watching on tv the other day, this phrase is where the modern "nero" originates from.
"Nero" also means "water" in Greek (modern Greek, as explained by d_tr). I was confused about whether you meant it as a Greek or Italian word by "mauro" that made the whole phrase sound Italian, at first. Sorry for the confusion :)
