Stir the water and bicarb soda together in a small bowl.
In a heavy saucepan, heat the sugar, buttermilk, butter and molasses to a boil, stirring to dissolve sugar. Reduce heat and stir in the bicarb soda mix. Simmer about 5 minutes, until golden and thickened. Remove from heat and add whiskey and vanilla.
Drizzle half the glaze over a hot cake, allowing it to soak in. Keep the rest in a sauce boat and reheat in the microwave just before serving.