Very low power electromagnetic waves with a frequency of 2.4 GHz can't cook anything. That's obvious, despite the heating effect such radiation has on water.
However, what if such an object containing water is exposed to this radiation for a long time?
Is there a chance of some further physical effect, however slight?
Bluetooth is already right in this frequency band. A typical microwave oven is 1000 W. Allowable exposure to Bluetooth energy is limited to 1.6 W/kg. So essentially this exact experiment is being run continuously over the entire developed world.
2.4 GHz is non-ionizing. The only known physical effect is tissue heating. At this level of exposure normal thermoregulation is capable of dissipating the heat and maintaining temperatures within normal physiological temperature fluctuations.
There are some published studies claiming adverse effects. However, to date no such studies have proved reproducible by subsequent independent investigators.
Should reproducible evidence of such adverse effects be substantiated then the IEC will revise its guidelines and tighten the limits (as it has in the past).
The only effect is heating. Microwaves are non-ionizing radiation which means they do not break chemical bonds. Microwaves have an energy of about 10^-5 eV. Ionizing radiation is defined by the FCC to start at 10 eV (molecular bond energies are usually 1-10 eV per bond, and 10 eV corresponds to 124 nm ultraviolet). The EPA definition is that ionizing radiation starts at 33 eV (the ionization energy for a molecule of water). Either way, 10^-5 eV is well under this limit.
Being under the limit doesn't mean that it takes more radiation to be ionizing, it means that it is never ionizing. If the energy of the photons is below this limit, then no amount of exposure will make it ionizing (unless you receive so much that you become so hot that you turn into a fine plasma, but people do not get vaporized when they turn on their cell phones' Bluetooth or stand next to their 2.4 GHz Wi-Fi router). You can't increase photon energy just by increasing the number of photons.
As long as your body is able to dissipate heat faster than it accumulates it, there are no negative effects whatsoever. For non-ionizing radiation, the test for whether it is harmful is easy: Are you burning or overheating due to radiative heating? Then you're receiving too much radiation. Otherwise it's fine.
Could there be unknown effects? Maybe, but there is no reputable research which shows any negative effects. The slight tissue heating you receive from the 2.4 GHz Wi-Fi or Bluetooth signals from your phone is dwarfed by the amount of tissue heating caused by your muscles holding the phone up.
As already pointed out, to date the only known potential biological effect of microwave oven electromagnetic radiation, which is non-ionizing radiation, is the heating of tissue. There are, as yet, no known long term non thermal effects, though studies continue.
In the U.S. the FDA requires that microwave leakage from ovens cannot exceed 5 mw/cm$^2$ measured 5 cm from the oven surface over the lifetime of the oven, which would be about 0.05 mw/cm$^2$ at a distance 50 cm from the surface. To date, these values are far below that known to cause biological harm.
For background information on the biological hazards of microwave radiation and the rationale behind the microwave oven leakage limits see https://www.sciencedirect.com/science/article/pii/S0362028X23009407?via%3Dihub
Hope this helps.
Exposure in itself may not be harmful / isn't harmful.
If you place a stone gently upon your skull, and leave it there for hours, you are certain to experience no harmful effects from this low-intensity, long-duration exposure of your head to the stone.
If the exposure-event was to be fast but short term, then one will definitely experience adverse effects.
The presence of the stone upon the head, or the 2.4 GHz does not have an accumulative effect as opposed to (for instance) heavy metal contamination in food/water.
