At some point the water bottle nut pulled out of the down tube on this Trek. That however did not stop the owner from riding it. What did eventually stop them was when the outer layer of carbon fiber started do de-laminate along the seam, down towards the bottom bracket.
After removing the layer of unidirectional that had come up, a patch was placed over the hole. This patch contained both carbon 3k weave and a layer of kevlar for extra strength.
The unidirectional structure was then rebuilt and a solid tube was formed. The location of the nut to be re-installed was then located and carefully drilled. After the edged of the hole were sealed up and the nut installed, a layer of glossy clear was added for looks and UV protection.