"The boy wants water."
Translation:Tá uisce ón mbuachaill.
I strongly second that! There needs to be a lesson that actually teaches the patterns. I do not have a clue about question structures, or the difference between Irish forms of "want" and "need" for that matter. Every time I think I've figured it out and type something in, it gets marked as wrong. I've started to just note down single sentence on a piece of paper and then just type it in when it comes up again. This is more than frustrating!
I think you're right. See: https://en.wiktionary.org/wiki/%C3%B3n#Contraction
It is always ón.
Táim is not considered a contraction, it is considered a synthetic form. There are many other synthetic forms used in other tenses and moods that are clearly not contractions, like bhíomar in the past tense, or bheifeá in the conditional - táim happens to look like a contraction, and it coincides with a contraction in English, but technically, it isn't.