I'm not a pilot, so I'll let others advise you how you put your bird in the water...
However, I was (past tense) a fully qualified survival instructor, who supervised ditching drills for many years. I also conducted (as part of my training) all sorts of water entry scenarios (including night drills in a storm).
So my advice is...
Don't ditch. And if you must...make sure your will is up to date.
Seriously, if you ditch in any thing but the most benign conditions, most of you will die.
Knowing what to do is very little use, unless you have practiced it, frequently, and in realistic conditions.
In calm, warm water, without any sort of injury, and with easy exit and flotation options, with help close at hand, you might make it.
Now start adding in the problems...
Can you get out of your wreckage and in the water...no. You die.
Are you injured or in shock...yes. You die.
Can you float..no. You die
Is the water cold? Yes. You die.
...
but I am wearing a correctly fitted water survival suit?? Really, are you.
But if you are, You'll die slowly.
Is the water rough...yes, you'll get seasick in minutes and you will want to die.
Enough...you get my point.
So
Don't fly over water unless you have a compelling reason.
Fly at a gliding height to reach land.
If you are out of reach of land, have your survival kit on!!
Practice getting out of the aircraft with your survival kit on.
Ensure you get a mayday out.
Ditch near a ship
Forget about food and water...you will be dead long before these become an issue.
But do ensure you are fed and fully hydrated before you fly.
My best mate flys low over the sea in a microlight. I've told him till I'm blue in the face if his engine stops it's game over. End of story