Aia is a locative. It means there, there it is, there are. My dictionary defines it as an idiom. Acting with i hea in this sentence, it comes to mean "where is." In other sentences, you wonʻt necessarily see it translated to There are toys on the floor, but shortened to The toys are on the floor. Thatʻs the pattern Iʻm seeing on DL, anyway.
This is nonsense. It constantly forces me to use the definite article "the water". Water is a classical example of a "mas noun" and therefore is usually not accolated with articles. Why is your program forcing me to use incorrect English? It would made sense only in form "Where is the water tap?" or "Where is the cup of water?" or alike. Correct your English!