Lemon vinegar is one of my favorite ingredients that can mix with milk, soda water, or even with hot water. In lemon vinegar, the acid from lemon melt into the acid in vinegar, and that helps improving your circulation, so it warm your body from inside. It also help your body to recover when you are tired too. Moreover, lemon vinegar makes your immune system work better, so this is what you need to have for the flu season.
This lemon vinegar is very easy to make.
You just need to wash and slice the lemon and mix with same weight of vinegar and sugar. Say you have 100 gram of lemon; what you need are 100 gram of vinegar and 100 grams of sugar mix all together in one bowl. Then, you can leave it 12 hours in the room temperature or 3 - 4 days in the refrigerator.
If you like the bitter taste, I recommend to have lemon skin on, but if you are not good with it, peel the lemon skin when you slice it.
Ref 1: http://cookpad.com/recipe/3664016
Ref 2: http://hotjupiter.net/lemonzu/