No, it is not safe to microwave an empty metal water bottle. Microwaving metal, including water bottles with metal components, can be extremely dangerous and cause serious damage to the bottle, microwave, and potentially harm you.
When metal is placed inside a microwave, it can create sparks and electrical arcing, leading to a fire hazard. Additionally, the microwave's electromagnetic waves can't pass through metal, causing the metal to reflect and absorb the microwaves, which can lead to localized high temperatures and potentially cause the metal to melt or catch fire.
Moreover, microwaving a metal water bottle could release toxic substances into the food or water inside, especially if the metal contains any coatings or linings that may contain harmful chemicals.
To ensure safety and avoid potential hazards, always check the manufacturer's instructions for your water bottle to see if it is microwave-safe. If there's any doubt about the materials used in the bottle or if it contains metal components, it's best to avoid microwaving it altogether. Instead, opt for microwave-safe containers made from glass, ceramic, or microwave-safe plastics.