t understand why it doesnt accept "senza" since as far as i can tell " senz` " is just the short for of the word above :(
I think it helps the sentence to flow better. It is more awkward on the tongue to say "senza acqua", as opposed to just combining the two by using only one 'a', thus "senz'acqua"
senz'acqua is pretty much self explanatory I would think, however maybe it's best to report mistakes like that. I suspect staff are keen to receive feedback to improve everyone's learning experience. I try to do so when I see things looking a little odd here.