[TeMPOraL]

Water is also a good RF screen, so such shield would also effectively blind and cripple the ship. Even discounting the energy use, no way they could keep that up continuously. Ramp-up time is probably large enough too (on the order of seconds), making surprise attacks very feasible. Not an ideal countermeasure, though I'm not sure what would be, beyond packing more ablative armor.

[dredmorbius]

If you're in a position to be aware of an imminent attack, ramp-time is probably within reason. Power reqirements are fairly modest by military standards -- a small fireboat can pump impresive quantities of water, and since the goal in defence / obscuring is to blind (and absorb energy), a finer atomised mist would be more effective. Filter and system fouling is likely a bigger concern.

True bolt-from-the-blue attacks are rare, though possible.

The spray profile could be modified to enable sensor detection, or alternative (off-ship, buoy, balloon, drone, ...) sensor placement could enable both eyes and shields.