I was curious if wifi would work under water and I couldn't find any clear answer online, so I did a quick experiment.
I packed my phone in a plastic bag and notet the signal strength at different depts of water in a plastic bin. I placed the phone on a water filled cup, to make sure there was water on all sides. Water level under the phone 5cm, sides minimum 10cm. Depth is measured from under the phone, so allow ~2cm for thickness of phone and air in the bag.
Tests at 2.4GHz:
No water: -54 dBm
On water filled cup: -53 dBm
Water to top of cup (0cm): -63 dBm
2cm -57 dBm
3cm -71 dBm
4cm -79 dBm
5cm -81 dBm
6cm -85 dBm
7cm -84 dBm
8cm -85 dBm
9cm -85 dBm
I didn't repeat the full series at 5GHz, but i measured -59dBm above water and -80dBm at 9cm.
It would be interesting to repeat this with an ESP32 under more controlled conditions..