Eventually water bottle mount threads go. If you’re lucky as me, the whole nut inside the frame will turn and then the flange on the outside of the tube will break off.
Crazy glue the threaded end into the tube. Clamp vise grips on the head of the screw to hold on to it while cutting.
Take a hacksaw and carefully cut off the head off the screw. Find a fibre locknut that will fit and screw it on carefully. Threads may be damaged so gradually turn the nut back and forth lightly with fingers until it screws on.
Find a metal water bottle holder that has a thin base so the nut will screw in far enough.
Use a nut driver and cautiously tighten the nut, careful not to break the crazy glued end loose.
Done! Never remove it again!