very, very good question...i've only been in the southwest for a little over a year and i'm assuming that there are many more mineral deposits in the drinking water than back where i'm from. i got the same deposits from crushed, bagged ice from fry's grocery store and i get some even from my fridge - but that could be from something else. i haven't looked and analyzed the deposits from sonic ice thoroughly because there was lots of it and it grossed me out. i don't find the same deposits in circle k ice, subway ice and the ice from my job. also, i've noticed that gas stations have some good ice, but the ice from most restaurants is bad. i don't know why that is. so...combined with the deposits and the grease smell, sonic in this area is on my "desperate" list.