Can water serve as a medium for intercontinental high speed data transfer? How?

Short answer:   I can think of lots of practical reasons why we shouldn't use just water as the medium for carrying information through electromagnetic waves.   In theory, you could possibly get something to work.  However, the invention of fiber optics essentially rendered the question useless, as optical fibers are excellent ways of carrying information long distances without compromising the readability of the signal. Long answer: Even neglecting the curavture of the Earth, which would be non-trivial when trying to propagate a beam all the way across the Pacific, e.g., you need a way to keep the information somewhat "coherent" (i.e., you would be able to read it on the other side).   The first problem you would come across is that if you just drop a radiating source of electromagnetic waves in the water, the radiation would spread in pretty much every direction.   This is a problem that is mostly solved; you could use Gaussian beams, which is what any laser that I know of uses, to help keep a mostly "straight" beam.   While laser spot sizes do grow the longer they are from the source, the rate of growth can be made very small through various means.  If you can therefore propagate a beam in a specific direction, you would then find that water, like most media, is dispersive - components of the wave that have different frequencies will propagate at slightly different speeds, and this can easily ruin your message if not accounted for well.   Like the previous issue, this one can likely be worked through with a bit of effort.  Next, water is slightly conductive, and thus the amplitude of the wave would decrease as it propagated forward.  You'd likely need places along the way to "buffer" the beam and increase its amplitude back up to something readable.  If you had all of that figured out, you'd likely still be in trouble because there is lots of stuff in the ocean, and electromagnetic waves easily scatter off of things like fish (and may kill them if the radiation is very intense, which it would likely need to be).   These are just problems I've thought of off the top of my head with propagating electromagnetic waves through the ocean; I'm sure there are many more. Luckily for our civilization, there is no need to worry, because there is a much easier solution called a waveguide.    The historical example of a waveguide is just a long, hollow tube of metal, but  a clever solution is to use a "glass" one.  This is the study of fiber optics, which you've probably heard of by name.    Fiber optic waveguides dissipate energy at a much slower rate than their historical metal counterparts, and are significantly cheaper to make.   Much modern communication happens along these fiber optic cables, strung out underneath the ocean.   I believe that the actual construction of these cables includes metal sheaths, but if these were not there, the electromagnetic fields would actually be nonnegligible in the space around the fiber optic waveguide, meaning that in a tiny sense, the water does indeed act as a medium for carrying the information (although it isn't the primary one).   It is not an uncommon phenomenon, by the way, for waves to propagate nicely along the interface between two different media; this is essentially why fiber optics works so well.

Technically you could, provided the water was laden with enough electrolytes to conduct a steady current, to say it would be any good sort of transfer rate and that you'd have all the packets received (if any) would be false. data likes transferring over organized media. Hence why a coherent beam of laser light will transfer much faster and cleaner than say, normal radio waves.

About water able to transmit information - as for maintaining or distroying health in a body - discovered by Dr Jacques Benveniste ( who tryed  to avoid baby's death. At this time Aids in blood was not systematically found ). At that time, and forgetting all his past discoveries, the Nobel prize was refused to him. Though as for scientific discoveries AND saving lives he was very entitled to it. Would it be possible to discuss about the possible " memory " or  " information transmission  " by water as now for instances " viruses " are recognized as " information or program  targeted to cell communications ". Many grateful thanks chalom rav