Qusay Kh. Al-Dulamey

The heating ability of an electromagnetic source depends on how well that radiation is absorbed.

At a few GHz, water displays significant absorption - and so a sufficiently powerful source can (as you point out) create temperature rises.

Short of reducing the power of the source, you can either change the material that you are interested in (what is it that is being heated?) or shield it in some way.

Do you have particular details of the situation that you can share?

Thank you very much