Do you actually want acetic acid? That's vinegar. If you're looking for something to use in Dosa batter instead of Eno salts, use citric acid. Eno salts is half bicarb and the rest mostly citric acid. I don't actually use it myself, not sure what its supposed to do for dosa batter, but I know lots of people do use it. If you are in the US, you can get citric acid in the canning section of a grocery store or department store like WalMart. Sometimes hardware stores will carry canning supplies in the fall, too. The brand I usually buy is Ball, the same guys who made the canning jars. Check WalMart, groceries, TruValue hardware stores, Ace hardware stores, or places like Tractor Supply company (seriously, that's a general store/hardware store, farm supplies, not really much to do with tractors at all, LOL!)