Pour water and vinegar into the saucepan, add granulated sugar. Bring everything to a boil, then turn off the heat and cook for another 10 minutes on low heat. After ten minutes you will have a sugar syrup.
Pour the cooked syrup into a cold bowl and leave to cool slightly, stir it occasionally.
After 5-6 minutes of mixing, the color of the syrup gradually changes to white and the mass begins to solidify. You are still occasionally mixing it.
After another 5-6 minutes you will reach the desired consistency.
If necessary, you can add food coloring and spread it on the cake. This amount of icing is enough for a cake with a diameter of approx. 9-10 in'. The icing on the cake will harden in less than 1 hour. If you need more icing, make it from a batch of 2 & 1/2 cups of sugar, 1 cup of water and 1 teaspoon of vinegar. In this case, cook for 15 minutes.