I don't see how you could have an allergy to water. But I don't claim to know that for certain.
However, calling water "aqua" isn't entirely misleading - the same list is used in all languages,* as far as I can see, so a Latin word that will be vaguely familiar from school chemistry lessons is quite likely better than an English one that will be totally unfamiliar to many/most. Of course, they could just translate the list, as with food ingredients, but there are two problems with that: 1) most chemicals have no common name in any language 2) having the same list for all means you can recognise an ingredient you know you are allergic to, wherever you may be.
Then again, the fact they do translate for Cyrillic, Arabic, etc, counteracts the second point (I don't know to what extent it's actually a translation, I expect it's more a transliteration).
*that use the Roman alphabet.