Here is the full list of all 12 Hydrophobia achievements worth 200 gamerscore. It takes around 6-8 hours to unlock all of the achievements on Xbox 360.
Complete the game.
Collect 50% of the medals.
Collect all documents and objects.
Collect all the medals.
Complete the Challenge Room.
Complete a hack.
Sweep 3 Malthusians off their feet with water.
Kill 5 Mathusians with fire or electricity.
Kill 2 Malthusians within a timed chain attack.
Save Chief Billingham.
Neutralize 10 Malthusians in underwater combat.
Drown a Malthusian.