You are correct, burning carbohydrate produces various combinations of C, CO and CO2, plus H2O. More importantly, the process of biological respiration takes sugar and effectively "burns" it in a series of controlled steps, but resulting in waste CO2, and water. The CO2 is literally breathed out, replenishing what the plants used to make the carbohydrates. The water is produced using oxygen gas as the final acceptor in the electron transport chain, so those molecules enter the population of other waters in our body, to be used like any other, or may be Incorporated directly into other molecules. Either way, it takes the place of one water molecule that would have been brought from the outside to fulfil the same function.
In essence, oxidative respiration is the biological mirror image of photosynthesis, in that each feeds the other in a beautiful meta-circle.