NY has brought this to us :
Do they use 2.4 GHz? I'd assumed/read somewhere that they didn't use a
resonant frequency of water for that very reason, and that 2.4 was only
available because no-one (eg military, broadcast) could use it for anything
else long-distance. On the other hand, with a dish aerial to concentrate the
available power into a narrower beam, maybe water attenuation can be overcome
sufficiently to transfer a usable signal at 20 km range.

Much longer distances have been managed than that.

I really don't follow how a copper tank full of water, can attenuate a
signal more than the same tank, but empty.