Nethuns's domain, spanning fresh springs, wells and rivers as fully as the open sea, marks a theological structure distinct from the more familiar Greek and Roman pattern, in which Poseidon and Neptune are overwhelmingly gods of the sea proper, with freshwater generally left to separate river gods and nymphs rather than folded into the chief maritime deity's own portfolio. This combined freshwater-and-sea structure has closer typological parallels elsewhere in the ancient Near East than in the classical Mediterranean immediately surrounding Etruria: the Mesopotamian god Enki, later Ea, likewise governs the sweet subterranean waters, the Abzu, understood as the ultimate source of rivers, springs and wells, alongside broader authority over waters generally, a structural resemblance comparative historians of ancient religion have noted as a recurring type, the single water god who unites fresh and salt water, found in scattered form across several ancient religious systems that developed independently.
Whether Nethuns's combined domain reflects genuine, if indirect, contact with Near Eastern religious ideas through the same trade networks that carried Phoenician material to Pyrgi, or whether it developed independently as one plausible way for a culture bounded by both a coastline and an inland network of springs to organize its water theology, is not something the surviving evidence can settle. The comparison at least shows that Nethuns's dual authority over fresh and salt water was not the only option ancient Mediterranean religions found available, and that Etruria's theological choice on this point set it apart from its immediate Greek and Roman neighbors even as it shared other features with them.