No, microwaving water does not make it radioactive. Microwaves work by generating electromagnetic waves that excite water molecules, causing them to vibrate and generate heat. This heating process does not introduce any radioactive substances into the water or make it radioactive.
Radioactivity is associated with the emission of ionizing radiation from unstable atomic nuclei. Microwaves do not generate ionizing radiation, so they do not have the ability to make substances radioactive.
However, it's important to note that microwaving water in a microwave-safe container can cause the water to become superheated. Superheated water is heated above its boiling point but does not appear to be boiling. When disturbed or when an object is placed in it, it can rapidly boil and potentially cause splashing or eruptive boiling. To avoid this, it is recommended to use caution when heating water in the microwave and to use microwave-safe containers and appropriate heating times.