You make some good points, and there’s also thermal issues.

The whole reason the datacentres use so much water is cooling all those processors.

Rejecting heat in space is super hard because you’re ultimately relying only on radiation (not enough matter for conduction/convection), no matter how many heavy/expensive/complex/maintenance-needing cooling systems you use.

But at least if it was able to be done, the heat would be 'outside the environment ’ as it were. The idea of using earth’s seas to cool datacentres on top of everything else does not sound ideal…