The art of looking foolish

I had an interesting encounter with a girl in a store the other day. It gets hot here in the afternoon and my throat was parched. "Agua por favor." (Water please - I politely articulated). "Como?" (What?) "Agua," I tried again. "Aga?" "No... agua. Gwa not ga. Agwa." "Oh agua," she retorted in a whydidn'tyousaysointhefirstplace type tone. "No tenemos." (We don't have any).
This kind of thing happens all the time. I have mastered the art of looking foolish. On a daily basis I am confronted with people looking at me with bemused expression wondering what rock I crawled out of. People aren't accustomed to a guero (white boy) speaking Spanish so they figure I must be speaking to them in my language. Therefore the lady must have thought I was asking for aga, a drink that is only available in Canada and the U.S.
What's worse is that I can understand most of what other people are saying, they just can't understand me. It´s like the Far Side cartoon where you get to see what the dog is thinking and he looks like he could be a Rhodes scholar but when he opens his mouth all he can say is "Woof woof." I would explain this joke in Spanish to the people here but the word for dog in Spanish is "perro" and I can't roll my rrs.