Is there a waterproof chdk feature??
There's a (float) feature, but it doesn't work in scripts.
The coolest feature is the ability to run scripts, and particularly Lua scripts. For your vacation, try setting the camera up on a mini tripod pointing at the kids in the pool, and run a script that takes shots every 5 seconds or so.
My favorite script is one that simply holds the shutter button down in continuous mode, and takes around 2 shots per second. Point the camera at the pool, and have everyone jump in. One picture is bound to be a good one.
--MUST BE IN CONTINUOUS MODE
print("Press <menu> to exit")
sleep(5000) -- time to get in front of the camera
press("shoot_full") -- continuous mode