This article is about a hypothetical ancient natlang family. For the languages of water elementals in fantasy settings, see Elemental languages.
The languages are all extinct and unattested, leaving only traces in other languages, mainly in form of the Old European hydronymy and substratum loanwords in the Indo-European languages of Central and Western Europe. The name "Aquan" is derived from Latin aqua 'water', a word that is limited to the westernmost branches of Indo-European (Italic, Celtic and Germanic) and also occurs in the Old European hydronymy, and may have been the Aquan common term for a watercourse.
According to the hypothesis, the Aquan languages were spoken in Copper Age Central and Western Europe and form a branch of the Indo-European family that separated from the rest of the family at an early date, together with the Anatolian languages or slightly earlier. He formerly assumed that Proto-Aquan may have been spoken around 5500 BC by the people whose archaeological remains are known as the Linear Pottery culture; see Europic for this obsolete hypothesis. These people, however, were genetically not very close to the Yamnaya people of Copper Age Ukraine and southern Russia who are widely identified with Proto-Indo-European; hence, he now considers this connection doubtful, instead proposing that Proto-Aquan resulted from the first wave of Indo-European expansions which would have brought the language to Central Europe ca. 3500 BC; Proto-Aquan would thus be a result of the same expansion movement that also resulted in the formation of the Anatolian branch. From there, the languages were carried west by the Bell Beaker culture. The last holdout of Aquan languages may have been in the British Isles, where these languages may have been the substratum responsible for the "un-Indo-European" appearance of the Insular Celtic languages.
The Aquan languages seem to preserve some archaic features of an early stage of Proto-Indo-European, such as a three-vowel system (*/a i u/) without ablaut (though this may be due to levelling of ablaut by a change which collapsed *e, *a and *o into single vowel), and perhaps a more agglutinating morphology (again, perhaps the result of analogical changes). Substratal evidence from the Insular Celtic languages may indicate that the insular branch, at least, may have been head-initial and active/stative, with a tendency to phonologically run together syntactically closely associated words (such as noun and adjective within a noun phrase).
Lately, Rhiemeier has abanoned this idea. The Old European hydronymy may be the onomastic equivalent of constellations or ley lines - an imaginary pattern emerging from the sheer mass of data which actually means nothing. Most of the names are accountable for from the languages known to have been spoken in the relevant locations in the Iron Age (mostly Celtic).