Electromagnetic transmissions do not travel well through water. (This is why submarines can be difficult to detect, or communicate with, when submerged.) You can take advantage of this by using water as a shielding material. It also slows down bullets really well, and shields you from most radiation.

Looks like those Gungans were really onto something, huh?

Transcript

R2-D2: Hey guys, I hate to blow your big "Nooo"s, but something actually important just happened.
R2-D2: On the bright side, our electronic signature just went way down.
R2-D2: Literally.
R2-D2: Also good, our X-wing is really well hidden.
R2-D2: On the less bright side, that dragonsnake is a real jerk.
Yoda: Ah, met the King, you did. Got bored of being King, I did.
Luke: What are you talking about?
R2-D2: To be fair, you did ask me to scuttle the ship.
Luke: You scuttled the ship?!
R2-D2: No no no no no...
Luke: Oh thank goodness.
R2-D2: It wasn't me, personally.